What does Genesis 17:6 mean?

God continues to reveal His covenant promise to make Abram, now renamed Abraham, into a father of multiple nations. God insists that He will make Abram fruitful, causing many offspring to come from him. Earlier in Genesis, God commanded men like Adam and Noah to be fruitful and multiply (Genesis 1:28; Genesis 9:1). Now God tells Abraham that He will make him fruitful and cause him to multiply. Unlike those earlier encounters, God has now taken on Himself the responsibility to create nations out of a single patriarch.

Finally, God reveals that kings will come from Abraham, which makes sense if Abraham is to father nations. Still, God means for Abraham to understand that he will be the patriarch of multiple royal lines. At this point in the conversation, Abraham most likely still believes that Ishmael, his only son through his servant girl Hagar, is meant to be the fulfillment of these promises (Genesis 16:2, 16). It won't be until later, when God renames Abraham's wife as Sarah, and declares that she will be the mother of many nations, that Abraham realizes that God is predicting a newborn baby for a 99-year-old man and an 89-year-old woman (Genesis 17:16–17).