L. M. Grant's Commentary on the Bible - Genesis 21:1-34
THE PROMISE FULFILLED IN ISAAC Now the grace of God bears its most important fruit in the history of Abraham. Sarah, at the unlikely age of 90 years, gives birth to Isaac, at the time God Himself had appointed (v.2). Though faith (that of Abraham) had waited long, till he was 100 years of age, yet grace (as seen in Sarah) eventually bore the fruit that God had promised. This pictures the fact that believers throughout the Old Testament had waited through centuries before the grace of God is... read more
Geneva Study Bible - Genesis 21:12
21:12 And God said unto Abraham, Let it not be grievous in thy sight because of the lad, and because of thy bondwoman; in all that Sarah hath said unto thee, hearken unto her voice; for in Isaac shall thy seed be {d} called.(d) The promised seed will be from Isaac, and not from Ishmael, Romans 9:7, Hebrews 11:18. read more