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God Keeps His Promises -- a study of Genesis 21

Updated: Jan 21, 2022

God keeps his promises and can be trusted.

Bible Study Ideas and Commentary for Genesis 21

God proved that He was faithful to keep even the most impossible-sounding promise. This faithfulness is the foundation of our trust in God because we know He will keep His promise to save us in Jesus Christ. [Then, please add a short section about responding to God’s faithfulness by our own giving.]

Who would have told Abraham that Sarah would nurse children? (21:7)

This weekly post started as a resource for Bible study leaders; I am slowing adding older posts for reference.

Getting Started: Things to Think About

What’s in a Name!

Last week-ish, we talked about the power of God’s changing the name of Abraham and Sarah. This week, we talk about the birth of Isaac, a word meaning “he laughs.” It’s a beautiful name that would always remind the parents of their laughter in mockery which God turned into laugher of joy. It was a reminder of God’s grace and love. So—what does your name mean? Go around the room and see what your class members’ names mean! Realize that people have generally stopped giving names based on meaning and started giving names based on popularity or the coolness factor (how else do you explain “Colt McCoy” or “D’Brickashaw Ferguson” which are some of the coolest names ever?). But you might still have fun going around the room. If anyone doesn’t know, try

  • (which is very thorough, but maybe too detailed; it has an awesome “family tree” function that shows you all the related names)

  • (which is really easy to use, but may not always be accurate)

Here’s my family.

  • Matthew: comes from the Greek name Matthaios, which comes from the Hebrew word Mattityahu, which means “Gift of Yahweh.”

  • Shelly: an Old English surname meaning “a clearing on a bank.” In America, it originally came from Michelle, which is the French feminine form of Michael, which is a Hebrew word meaning “Who is like God?”

  • Micah: a Hebrew contraction of Micaiah, which means “Who is like Yahweh?”

  • Sarah: as we know, is the Hebrew word for “Princess.”

How fun is that exercise!

Dreams, Big Dreams, and the Bucket List.

Even though Sarah put up a good front, you can tell by her reaction that she was delighted to have a child. For her, God’s plan coincided with a personal dream. And those are the best dreams! Talk to your class about their biggest dreams. What do they want to accomplish in their lifetime (this is often different than a bucket list, so keep that in mind)? Some of our dreams are more self-oriented than anything, but we’ll find that some of them can absolutely line up with God’s purposes for His children. We want to encourage and pray for those dreams! I think it would be exciting to see God help one of our class members fulfill his or her dream this year, don’t you?

Teaching Favor: Include a Stewardship Emphasis

David is preaching on the “grace of giving” on Sunday. We actually learn the concept of both the tithe and the offering directly from Abraham, so I would love to reinforce David’s message in our Sunday School lesson. I would ask you to save 10-15 minutes to shift gears to this secondary purpose: “God has fulfilled His promises to us; what can we give back to Him in our gratitude?” This is a lesson for all ages, and one that we want to emphasize for parents to teach and model for their children.

A Short Primer on Giving

David will be preaching on giving next week, and we would both really like all of our Sunday School groups to inject a short lesson on giving. You have three connections: the Tithe, the sacrifice of Isaac, and trust. Your easiest connection is that we learn through Abraham that we can trust God to keep His promises and take care of us, therefore we should trust Him with our giving.

Save about 10-15 minutes at the end of class and make this transition: “In the sermon today, David is going to talk about the grace of giving. More than anyone else in the bible, Abraham shows us why giving is a grace.” Then, you can make two points. (1) Have someone read Genesis 14:18-20 (about Melchizedek) and say, “God blessed Abraham, and in response, Abraham gave a tithe.” If anyone has questions about tithe, use the next page. The point is really simple: Abraham realized that everything he has was a blessing from God, so giving back the tithe was the least he could do. (2) Have someone read Genesis 22:2 (about Isaac) and say, “We’re going to talk about this in more detail next week, but today we can say that God has the right to demand anything and everything from us, but in grace He does not. Abraham learned that lesson on our behalf. Our response should be that out of gratitude, we give joyfully to God our offerings of thanksgiving.” That covers both tithes and offerings!

Finally, bring up a powerful example from the New Testament of one who was not like Abraham: the rich young ruler of Mark 10:17-23. Have someone read those verses, then focus on the last few:

Then, looking at him, Jesus loved him and said to him, “You lack one thing: Go, sell all you have and give to the poor, and you will have treasure in heaven. Then come, follow Me.” But he was stunned at this demand, and he went away grieving, because he had many possessions. Jesus looked around and said to His disciples, “How hard it is for those who have wealth to enter the kingdom of God!”

Ask the question, “Which would be harder for you: sacrifice your child or sell everything you have?” That should be easy! The point is that God has not and will not ask us to do either, but those extremes are designed to illustrate a very important truth: God has given everything to us, and God has sacrificed His own Son for us. What are we not willing to give back to God? What is more important to us than God? Just like with the rich young ruler, Jesus will find that thing and ask it from us. He asks gently and lovingly because He wants us to give it away freely.

Do you see how that works? The question that we learn from Abraham is not “What do I have to give?” but “What can I give?” The tithe is a good place to start. I do believe the tithe goes to the local church, but this isn’t a time to get legalistic. I do want to say this, though—while we are called to give of our time, talents, energy, and creativity to God, the lesson of Abraham is one of a material gift. We aren’t necessarily talking about money! That could be important to know. But in both cases we are talking about a material good. In the case of Melchizedek, it says that Abraham gave him a tenth of everything. In the case of Isaac, Abraham sacrificed the ram that God Himself provided. Abraham took a gift and gave it back to God. Both of those offerings were apparently acceptable to God!


Part 1: God’s Promise Realized (Genesis 21:1-2)

The Lord came to Sarah as He had said, and the Lord did for Sarah what He had promised. Sarah became pregnant and bore a son to Abraham in his old age, at the appointed time God had told him.

Let me just try to hit a few things the Leader Guide doesn’t completely cover. The word here for “came to” literally means “to visit.” It’s a little different than when the angel told Mary that the Holy Spirit would come over her. In that case, the pregnancy was miraculous. In this case, God simply needed to supernaturally assist a natural pregnancy by giving the now-old Sarah the physical strength to bring a healthy child to term. It is made clear that this pregnancy would not have happened without the Lord’s help; God gets the glory for this miracle. Really, everything about these verses points back to God: God’s promise, God’s timing, God’s plan. So, even though we might be tempted to say that Abraham and Sarah had a child “late in life,” in reality they had this child “at just the right time.” It’s impossible to speculate why exactly God waited until they were so old to do this. Yes, on the one hand it showed all of their people the power of Abraham’s God. And it is also likely that they simply weren’t ready for the challenges that faced them. But who knows what other mysterious considerations were at work in the background . . . What about that visit to Abimelech? How would have a younger Sarah have treated Isaac? I really don’t know, but this timing was right.

Your leader guide implies that the 25-year wait itself was the real driver, and suggests you talk about long waits for prayers to be answered. I like that.


Aside: Melchizedek and The Tithe

The first reference we have to a “tithe” is with Melchizedek. The word means “tenth” and was actually a common religious practice in the ancient Near East. Jacob, for example, may not have known anything about Abraham’s tithe when he pledged his own tithe to God in Gen 28:22! Before the Law, tithes were associated with harvest festivals (when people had 10% of something to give). In the Law, the tithe shifted in function to something more like a “tax” in our day. God commanded that the tithe be used to support the priests (who were not allowed to own land off of which they could make a living) and care for strangers, widows, and orphans. Every third year, the tithe was to stay in the local town to make sure that local needs were met (Deut 26). After the Exile, Nehemiah instructed that local Levites collect the tithe and send a tenth of the tithe on to Jerusalem (kind of like how our church sends a portion of our tithes to the CP). The rules were very strict in the Old Testament about the amount, though, making the tithe a tax.

Note that in the New Testament, although Jesus does commend the tithe (Matt 23:23), most of the references to giving are of far more than a tithe! The tithe was not just about produce but about one’s total income, and gifts and offerings on top of the tithe were expected. Eventually in the medieval Catholic church, the tithe became law again, and they wrote a great many laws about tithes of pro-duce, of labor, of livestock, and what went to the local priest and what went to the vicar. The demand of the tithe led in part to the English Civil War in the 1640s. I strongly advise that we stay away from a legalistic approach to giving! What someone gives is between he and God. But it is important that we teach our church members and our children to give of our material possessions (i.e. money) to God in a significant, regular, and measurable way.

Bonus Aside: Who Is Sarah?

I have spoken somewhat harshly of Sarah, particularly in her mistreatment of Hagar. I also gave her a bit of a pass with respect to the incredible challenge of having a child at a very advanced age. We really don’t know very much about her. She was Abraham’s half-sister (a marriage relationship that actually wasn’t uncommon in those days). When she was 65, Abraham led her on their journey with God. Surely we can speak highly of her here, in her willingness to follow her husband to, well, God knows where! Twice, she allowed Abraham to lie about her identity to preserve his life, ending up both times married to a strange man. That says something, too! I think.

Then we find her willingness to give her maid to Abraham in order to fulfill God’s promise. Of course, she ended up being so jealous that she mistreated both Hagar and Ishmael. That’s not good. She also laughed when God told her she would have a son. Abraham didn’t tell her that God commanded him to sacrifice Isaac. She lived for 36 years after the birth of Isaac, dying before he was married.

The New Testament really doesn’t say much of anything about her at all. Romans 4:19 mentions her barrenness, Romans 9:9 says her conception was proof of God’s power, Gal 4:21-31 allegorically contrasts her with Hagar, Heb 11:11 lauds her faith, and 1 Pet 3:6 called her a model of submission to a husband.

In summary, we don’t know a whole lot about her, and the little we do know involves trust issues, faith issues, lying issues, and jealousy issues. But before we jump on her too quickly, realize that she was following the lead of her husband. I take the story of Sarah as proof of God using truly ordinary people to bring about his promises.


Part 2: God’s Promise Remembered (Genesis 21:3-7)

Abraham named his son who was born to him—the one Sarah bore to him—Isaac. When his son Isaac was eight days old, Abraham circumcised him, as God had commanded him. Abraham was 100 years old when his son Isaac was born to him. Sarah said, “God has made me laugh, and everyone who hears will laugh with me.” She also said, “Who would have told Abraham that Sarah would nurse children? Yet I have borne a son for him in his old age.”

God had already commanded Abraham to name the boy Isaac, so this isn’t a sur-prise. It’s simply clarified for us why God chose that name: a constant reminder that He is greater than our doubt. And yet, this isn’t a rub-our-nose-in-it reminder, but one of grace, love, and hope. This name would bring joy to the parents. So let me put a twist on our opening exercise and turn it to nick-names. While we give regular names based on how we like them, we often give nick-names based on a character trait. Sadly, they are often intended to be mean, but they can also be fun and even encouraging. I’ve heard some great stories of nick-names around here that are uplifting; if you have anything like that in your class, please share!

Then we have the reference to circumcision (I'll talk about it below). What you might not remember (unless you really, really like to read Leviticus) is that the 8th day is actually thought of as 7+1. There are 7 days for purification (Lev 12), so the circumcision can happen on the 8th day.

And also make sure to give Sarah credit (if you have given her a hard time like I have). She got it. Her doubt, her fear, all of it was replaced with the understanding and belief in God’s provision. Because David just preached about service, I really like the leader guide question: what excuses do you give for not serving the Lord, and how does Sarah counter them? It doesn’t matter how old you are or how much you’ve doubted . . .


Aside: Abimelech—Here We Go Again

We’re going to skip the story of Abimelech in chapter 20, but I think it’s worth pointing out. It’ll sound really familiar. Abraham moved to the arid region of the Negev, and there told everybody that Sarah was his sister. A local king took her as his wife, only to have God place a curse on his house and speak to him in a dream. Needless to say, Abimelech was extremely upset with Abraham upon finding out the truth, especially since Abimelech had done nothing wrong! Abraham mum-bled some lame excuse, and Abimelech gave them 1000 shekels of silver and a bunch of livestock to go away.

As pathetic as it is, I love this story for what it says about Abraham. Abraham is the great hero of our faith. Yet along his journey to spiritual maturity, he was a colossal screw-up! I identify with him, and I am also encouraged not to make those mistakes. There are a few lessons in here, not that you'll have time to go through them this week! How do we relate to Abraham: his awful relapse? his fear? his fibbing? his testing of God’s promise? the irony of him needed to be rescued and have mercy upon by a stranger? At the same time, you can also talk about Abimelech—someone used by God to set you straight.

Finally, there is the background of prejudice. Abraham made his decision to lie based on the fear that Abimelech would kill him otherwise. It doesn’t sound to me like he would have been in too much danger! How many times have we jumped to judgment on a situation or a group of people only to find out we were wrong, and maybe be really embarrassed?

Bonus Aside: Circumcision and Baptism

Not to be intentionally gross, but circumcision is the act of removing the male foreskin. This was originally carried out by the father on the 8th day with a flint knife. Later, experts were mercifully employed. Jews were not the only circumcised people (see Jer 9:25-26). Later, God explained that circumcision was intended to be a symbol of obedience and listening to God (Jer 4:4; you "circumcise your ear" in order to hear the Lord, Jer 6:10).

Infant baptism originally had nothing to do with circumcision. There was a faulty belief that baptism washed away sin, which is why people waited until their deathbed to be baptized. But due to high infant mortality, parents began baptizing their infants to be safe. A corresponding doctrine was developed that baptism washed away “original sin” which eventually was codified to encourage all babies to be baptized.

Early Reformers like Luther and Calvin wanted to step away from that Roman Catholic teaching, but they faced a great deal of popular pressure from parents who were worried about their infant’s salvation. So a new development came about in the 1500s (usually based on Col 2 or the like) saying that the Church was the new Israel, so baptism was the new circumcision. As circumcision happened of infants, so should baptism.

Never mind that girls were not circumcised, and that baptism was a response of faith (leading Reformers to keep the office of godparent as someone who would vouch for or speak for the infant’s faith). If you ever have someone say that baptism is just like circumcision, send them my way!


Part 3: God’s Promise Rejoiced (Genesis 21:8)

The child grew and was weaned, and Abraham held a great feast on the day Isaac was weaned.

Your leader guide talks about this timing of this celebration and its importance in this culture. However, I read elsewhere exactly why LifeWay chose to break the lesson as they did. If you read on in the Bible, you will see that this event became the occasion for Sarah to decide to throw out Hagar and Ishmael—a very significant and heartbreaking thing. But LifeWay rightly points out that the intention for this event was to celebrate, regardless of how it actually turned out. I covered a few weeks ago that late-in-life pregnancies are at even higher risk for some sort of significant health issue—all the more reason to celebrate Isaac’s healthy growth. A couple of year’s into Isaac’s life and Abraham had not lost any of the joy over God’s kept promise.

The application here is that we should all remember to celebrate God’s blessings. We should teach our children to celebrate them. That way, when we go through the dry times in life, we have them to look back on. Your leader guide suggests mentioning recently-answered prayers in your group; I think that’s a good idea, and it’s right in line with several of the other exercises they have suggested recently.

Think about it. Abraham and Sarah had to wait 25 years for God to keep this promise (remember that everything happened exactly when God said it would, but it sure seemed like a long time!). During that delay, they run in fear down to Egypt where they get into a mess, they watch their nephew’s home get destroyed and quite possibly hear what else happened, then they run in fear to another kingdom where they get in another mess. And who knows how many other countless dramas they experienced along the way. What did they have to sustain them? Three different promises from God; nothing tangible to hang on to. We have a little more than that. We have the proof of God’s promise to us through the Holy Spirit in our hearts. We need to celebrate the victories God has given us in our spiritual lives and families! One closing exercise might be to tell one another about those steps of spiritual growth we have been blessed to take and what they mean to us.

One resource suggested having everyone bring in a baby picture of themselves that you put on a board to guess identities. That could sure be fun. I would put a twist on it, though—have everyone bring in a picture of their children, grandchildren, nieces or nephews, any child in their life who is still pre-teen. Every child represents a promise from God, an unlimited future if possibility. No matter how old we are, we still can play a tremendous role in that child’s direction. Have your group members talk about the future possibilities for that child (in only positive terms!) and what you need to do to help bring that future about.

Then, use that topic as a transition into a time on stewardship as one of the things we need to teach is giving!

Some of your group members will probably complain that this lesson is repetitive of things we have already discussed, and they would be right. In this case, though, that’s the point. Abraham’s relationship with God is utterly foundational to everything we know and believe as Christians. God made Abraham an impossible promise. If He didn’t keep that promise, nothing else mattered! Even better, God used that promise to bring about His people, which is how He chose to bring about Je-sus. Everything we have starts with God keeping this promise.

In one resource on this passage, the writer told a story that made a point that really got to me. He talked about when his father died and preparing to preach the funeral sermon. He really highlighted his dad’s honesty, integrity, and faithfulness, talking about the valuable lessons he had learned from his dad and how much he appreciated him as a man. That’s wonderful and powerful, but he took it to another level:

“The true significance of the moment was that dad had not just died; he had died in Christ. Dad was indeed a man of his word, but even more he had placed his faith in Christ. Our God is true to His word, more so than any man. He is faithful. What He promises, He fulfills. We were able to celebrate dad’s homegoing precisely because the Lord promised that those who believe in Him, though they die, shall yet live (John 11:25).”

That’s why this lesson is so important. This is how we know we can trust God. We’re not just trusting Him with tomorrow’s meal, we’re trusting Him with our eternal souls. Our children’s eternal souls. That’s a big, big deal. Thank God that we can trust Him!


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