Genesis 21:1-2 God followed through and kept His word in which Sarah bore Abraham a son at the time of which God spoke.
Genesis 21:3 The text clarifies that this son, Isaac, was of Abraham and Sarah’s flesh and blood.
Genesis 21:4-5 Abraham, 100 years old at the time of Isaac’s birth, obeyed God’s command and had Isaac circumcised on the 8th day of Isaac’s life.
Genesis 21:7 Not only did Sarah produce a child in her old age, but was able to nurse the baby also.
Genesis 21:7 Isaac was probably around 2 or 3 years old when he was weaned.
Genesis 21:9-10 Sarah noted that Ishmael belittled Isaac, most likely making fun of Isaac’s role as being Abraham’s heir. Seeing that there would be a rivalry between the two brothers suggested to Sarah that Ishmael and her mother had to leave. Legal codes of Abraham’s day—e.g., of Nuzi and of Hammurabi—forbade the putting out of a handmaiden’s son if a rightful, natural heir was born. Sarah’s request thus offended social law, but God gave His approval.
Genesis 21:11-13 Though it saddened Abraham to depart from his son Ishmael, who at this time was around 17 years old (a customary time for sons to go out to set up their own lives) and that he loved just as much as Isaac, the Lord took Sarah’s side and told him to listen to Sarah’s voice. Abraham did not see at the time that Ishmael would threaten Isaac’s inheritance, especially through his mother, Hagar. God repeated his promise that though Ishmael and his mother had to go, he would bless Ishmael also.
Genesis 21:14 Abraham obeyed the Lord immediately for he took action very early the next morning sending them off with only bread and water.
Genesis 21:18-19 Ishmael cried out in thirst and would have died if the Lord had not intervened. The Lord kept His promise He made to Abraham concerning Ishmael and provided for them in the wilderness.
Genesis 21:22-24 Abimelech, seeing that God had blessed and favored Abraham, feared that some future curse would come upon him and his people, so he made a peace treaty with Abraham and his offspring to help secure himself and his offspring.
Genesis 21:25-31 Because of a dispute that arose over Abimelech’s people stealing a well that clearly belonged to Abraham’s people, Abraham made a covenant with Abimelech, along with seven ewe lambs as a witness that the well belonged to Abraham. They named the place Beersheba.
Genesis 21:33-34 Abraham planted a tree in Beersheba as a functioning reminder of the treaty and as a marker of one of Abraham’s worship sites.