Genesis 21:7
And 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. And 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.
Sarah bore Abraham a son in their old age at the appointed time, Abraham being a hundred and Sarah being ninety, wholly by God's promise, power and word and not by human ability or by the earlier plan to gain an heir through Hagar. It was a wonderful surprise that filled her with joy in God, the child was named Isaac for rejoicing and she herself nursed him though bearing children had once seemed impossible. The promised Seed was to come through Isaac by the free lawful wife and not through Ishmael, preserving the chosen family line from which the Messiah would descend. Isaac was the child of promise born of the Spirit through trust in Him who promised, in contrast to Ishmael born after the flesh as the fruit of unbelief and human devising. Sarah as the freewoman mother of Isaac set against Hagar the bondwoman mother of Ishmael portrays the two covenants and the two peoples, while Ishmael's mocking and exclusion shows that the son of the bondwoman was not to share the heirship, for in Isaac the seed was to be called.
Miraculous Birth in Old Age
Sarah bore Abraham a son in their old age at the time God had appointed, despite her former barrenness. Abraham was a hundred years old and Sarah was ninety when the promised son was born. The birth came wholly by God's promise, purpose, plan, power and creative word, for the flesh had no power to bring him forth until God's all-powerful word was given. It was not by human planning, ability or schemes, such as the arrangement thirteen years earlier between Abraham and Sarah to provide an heir through Hagar to meet a seeming failure on God's part, which did not fulfill the promise or meet the situation at all.
The birth was a surprising, wonderful event that caused Sarah great joy and rejoicing in God. The son was duly named Isaac, meaning laughter or rejoicing, and circumcised. Sarah herself nursed him, though bearing children had once seemed impossible, and the event brought wonder at God's dealings with Abraham and Sarah.
The birth occurred just after Sodom was destroyed. The feast when Isaac was weaned came about five years after his birth. Since he was born twenty-five years after the promise to Abraham, Ishmael's mocking at the feast occurred thirty years after the promise, marks the beginning of the four hundred years of affliction, and is called persecution.
Promised Seed and Covenants
The promised Seed was to come through Isaac rather than Ishmael, through Abraham's lawful, free wife according to God's law and promise, not by human devising. Sarah bore the promised son at the time God had appointed despite her old age and former barrenness, wholly by God's promise, purpose, plan, power and all-powerful creative word, and the flesh had no power to bring him forth until that word was given. This preserved the chosen line through Abraham's own family, whose providential role was to preserve that line, and Abraham's fatherhood of Isaac establishes him as ancestor of the Messiah as traced in Matthew's genealogy. The son was duly named Isaac and circumcised, confirming the true seed comes only in this way.
Isaac was the miraculous child of promise, begotten of the Word and born of the Spirit, not a child of the flesh. Sarah received power to conceive when past age because she trusted the One who had promised, so the glory for his birth belonged to God and his birth was contrary to human expectations, planning and ability. This contrasts with Ishmael, born after the flesh as the fruit of unbelief and human devising, such as Abraham's arrangement to provide an heir through Hagar, which did not fulfill the promise. Isaac's birth therefore represents the freedom given to those who trust God's promises.
Sarah the freewoman as mother of Isaac, in contrast to Hagar the maidservant as mother of Ishmael, gives the basis for the account of Abraham's family as the two covenants. The sons of Sarah and Hagar represent the children of the two covenants, testaments or dispensations. They set forth the two systems, typical and antitypical, and the two peoples, literal Israel and true Israel, Jews and Gentiles, as representatives of the Lord and His work in two special periods of its development in the earth.
Isaac's birth displaced Ishmael from succeeding to Abraham's titles and inheritance. Ishmael had been born through Hagar thirteen years earlier by arrangement between Abraham and Sarah to meet a seeming failure on God's part, when Abraham was a hundred years old at Isaac's birth and Sarah was ninety, and that earlier birth did not fulfill the promise or meet the situation at all. When Ishmael mocked Isaac at the feast celebrating his birth, Sarah perceived more clearly that Ishmael must not share the heirship and break up the home, and demanded that the bondwoman and her son be cast out. That casting out broke Ishmael's bond of heirship and left him and his mother in bondage indeed, and God commanded Abraham to hearken to Sarah's voice because in Isaac his seed would be called.
The account belongs to God's progressive and providential dealings with Abraham, called the father of the faithful, presenting repeated lessons in faith and to be read with the Promised Seed in mind. Isaac's birth in Abraham's old age was a surprising cause for Sarah's joy, his name means laughter or rejoicing, and his birth illustrates the birth of Christ. Like Christ's birth, it was a step toward fulfillment of the promise to Abraham but not its completion, which comes when Christ returns and the dead are raised.
Faith Lessons for Life
Trust in the word of God is taught when barren Sarah gives birth to Abraham's promised child through his own family in old age, schooling Abraham to trust what God had spoken. The birth came by the power and promise of God contrary to human expectation, not by human ability or planning. It was not the result of human schemes such as the attempt thirteen years earlier to provide an heir through Hagar, but it fulfilled God's promise and represents the freedom given to those who trust God's promises. The surrounding history stands as an example of the unhappiness caused by polygamy in Abraham's family. The verse belongs among the biblical examples recognizing the worth of children, with Isaac's life demonstrating the value of true education and proper training.