Without question Gen. 21 is a crucial chapter in the Abraham saga. Here, finally, and after many many anxious years of waiting we hear “and the Lord singled out Sarah as he had said, and the Lord did for Sarah as he had spoken. And Sarah conceived and bore a son to Abraham in his old age at the set time that God had spoken to him.“. If Abraham knew a set time, he certainly didn’t act like it, or didn’t fully believe it, as it was too far off from the time of the initial promise of offspring. And Abraham named the child Itzak=she laughs, and he circumcises him on the 8th day as commanded , and all this happened when Abraham had turned 100 (though I still wonder if they were counting years on a lunar rather than a solar calendar)! Since there are 354 days in a lunar year, if they were counting on that system 100 lunar year= 1,100 days less, which is to say about 3 years less, not a big difference.
Sarah says ‘Laughter has God made me, whoever hears will laugh at me’. There is ambiguity to the Hebrew noun tsehoq=laughter. This could be laughter out of joy, but that same word can mean ‘mockery’, all who hear may mock Sarah, or perhaps laugh with her. It being a patriarchal situation it would matter that she bore Abraham a son ‘in his old age’. Notice the reversal, previously she called herself all wrinkled and dried up, now she speaks of suckling and weaning a son. God can make a way where there seems to be no way. So Abraham celebrates a big feast at the weaning of Isaac. This simply prepares for what’s next, namely the laughter of Ishmael the son of Hagar over the new infant son of Abraham, and Sarah cannot abide that response and says to Abraham ‘drive out the slavegirl and her son, for he shall not inherit with my son Isaac. And perhaps surprisingly God counsels Abraham to do what Sarah asks, since Ishmael will not be the seed through whom Abraham will be acclaimed. Nevertheless, God will make Ishmael into a nation as well since he is Abraham’s seed.
Now this story becomes important in Gal. 4 when Paul is contrasting the Mosaic with the Abrahamic covenants, and makes a big deal about the Hebrew saying seed singular here, which in a surprising turn of events he refers singularly to Jesus– THE SEED of Abraham. What is interesting about the Hebrew of vs. 13 is while seed seems to be a collective noun=offspring, in the second half of the verse ‘seed’ refers specifically to Ishmael, and it makes clear that Paul is not just making up the idea that ‘seed’ could refer to a particular individual, or even that the phrase ‘Abraham’s seed refers to Abraham’s own contribution to his own offspring, which is singular (not seeds in a prebiological world where they don’t know about semen and its many components).
So Abraham gets up early the next morning, gives a skin of water and bread to Hagar for her to carry them on her shoulder, and sent them off into the wilderness of Beersheba. But when the water is running out Hagar despairs, flings Ishmael under a bush as she doesn’t want to see her little child die, and she wept. But God heard the voice of the lad, and God’s messenger tells Hagar not to despair as God will make her son a great nation, and God opened her eyes to see the well at Beersheba (noting that Be’er means well). She fills the skin, gives it to Ishmael, and long story short, he becomes a good archer, dwelling in the wilderness of Paran, which apparently extends from Petra down to Midian. This is important even today because Ishmael is thought to be the ancestor of northern Arab tribes, who in turn involved the ancestry of Mohammed himself. Note that our text says Hagar found him a wife in Egypt, herself being an Egyptian.
Suddenly the text shifts back to the story of Abimelech, another good reason to think that this saga is composed of various individual traditions which have been edited together later. The anachronism at the end of the chapter, referring this territory to the ‘land of the Philistines’ who were by no means in the land yet, being a sea people probably ultimately from Crete, reveals to us just how much later these things were edited together. The Philistines do not show up in the land before 1200 B.C. or about 200 years before King David. But as for Abraham, he lived at least 700 years earlier.
So near the end of Gen. 21, Abimelech, having noted that God had been blessing Abraham and his flocks, and he wants an oath that Abraham, as his tribe increases will deal kindly with Abimelech’s people, as he has done with Abraham’s. Abraham says he will swear it, but while they are negotiating he criticizes the seizing of a well he had dug by Abimelech’s servants. Abimelech pleads ignorance, indicating he did not tell his servants to take this liberty. And as it turns out, this is the well Hagar had previously seen— at Beersheba, which means either well of the oath, or well of the seven. And the etymology is explains because Abraham sets apart and gives Abimelech seven ewes as a witness that Abraham had dug that well. And so they both swore, sealing their deal. Abraham throughout his existence since the call of God on his life was a nomad, a sojourner in various places in the land, and at Beersheba (which later become the southern border of Biblical Israel) he planted a Tamarisk=Oak and there invoked God’s name, the everlasting God.