Summary: God delivers Isaac to Abraham proving His faithfulness and revealing more of the promise for a Redeemer!
Adam disobeyed God bringing sin and death into the world, but God promised a Redeemer, and Abraham’s story reveals a little of how that promise comes to pass. At the age of 75 he left Haran (Gen. 12:4) to go to a strange land where he was promised a son; he waited about 10 years (Gen. 16:16) before growing tired of waiting and he had a son on his own, but God’s plan and promise didn’t change and Abraham’s son was rejected (Gen. 17:18-21). He endures another long period of 14 years until he’s 100 years old and finally the moment comes:
And the LORD visited Sarah as he had said, and the LORD did unto Sarah as he had spoken. 2For Sarah conceived, and bare Abraham a son in his old age, at the set time of which God had spoken to him.
God’s promise was right on God’s time—Abraham couldn’t rush it, and God wouldn’t delay it. And there was a reason for the wait: the son of the promise had to be born under supernatural circumstances. It was no miracle when Hagar got pregnant, but for 90 year-old Sarah to have a child is something only God could do.
3And Abraham called the name of his son that was born unto him, whom Sarah bare to him, Isaac. 4And Abraham circumcised his son Isaac being eight days old, as God had commanded him. 5And Abraham was an hundred years old, when his son Isaac was born unto him. 6And Sarah said, God hath made me to laugh, so that all that hear will laugh with me.
This is the name God told him to give him (17:19), and it means “he laughs.” It’s appropriate since Abraham and Sarah both laughed when they heard the promise, and Sarah now laughs in joy and all who hear will join her. It’s important to remember that this is part of the promise of a Redeemer who will remove the curse. Everything is done in sorrow for the time being (Gen. 3:16-17), but when the true Son is given there is much reason for joyous laughter!
7And she said, Who would have said unto Abraham, that Sarah should have given children suck? for I have born him a son in his old age.
No one would have thought this was possible a year ago (not even she had believed it), but God made it happen.
No one would have thought that Sarah would be able to nurse a child, but, yet again, God made it happen.
Even though these two had grown old, God was able to give them the pleasures of parenthood because nothing is impossible with Him. When we think of this relation to the promise it’s easy to see that God is able to give us what we can’t do for ourselves.
8And the child grew, and was weaned: and Abraham made a great feast the same day that Isaac was weaned. 9And Sarah saw the son of Hagar the Egyptian, which she had born unto Abraham, mocking.
By now Ishmael is about 16 and Isaac is probably about 2. It doesn’t tell us how or why Ishmael mocks, but in Galatians 4:29 Paul calls it persecution; the persecution faced by the early church was the same as what Isaac faced from Ishmael. It’s not just a little brotherly teasing—Ishmael hated and despised Isaac, and this too was promised of God (Gen. 16:12).
10Wherefore she said unto Abraham, Cast out this bondwoman and her son: for the son of this bondwoman shall not be heir with my son, even with Isaac.
Hagar had also despised Sarah (Gen. 16:4) and there’s no indication that anything’s changed. Ishmael should get some of the inheritance, Sarah won’t stand for it. Instead she commands Abraham to get rid of her and Ishmael so that Isaac will have it all to himself. This all sounds very harsh and maybe even impulsive, but we must keep the allegory in mind. In Galatians 4:22-31 Paul explicitly says that Hagar and Ismael are an allegory of those who are born of the flesh and Sarah and Isaac are an allegory for those who are of the promise. The sons of the promise receive the inheritance, but the sons of the slave woman are cast out. There is laughing and joy for the sons of God, but there is only sorrow and trouble for the world.
But that doesn’t make things easy for Abraham:
11And the thing was very grievous in Abraham's sight because of his son.
It’s easy to forget that Abraham saw Ishmael as his firstborn son, and he loves him. It wasn’t too long ago that he asked God to let Ishmael be the son of the promise (17:18). He would have been just fine without Isaac, so this is a cause of heartache for him, and he doesn’t want to do it.