As we continue through Genesis 17, new facts emerge. God and Abraham are discussing the conditions of their relationship. God required he live a blameless life before Him and presented the promises, finally requiring of him, the act of circumcision, to seal the deal. But there was still more God had to communicate about His plan regarding Sarah, Ishmael and Isaac.
Sarah
Sarai, like Abram, received a name change. God would bless Sarah and give her a son. She would be the mother of nations and kings of peoples would come from her. Abraham fell on his face and laughed. It was beyond his comprehension.
Ishmael
As for Ishmael, he was Abraham’s son. Abraham loved him as a son and wanted God to accept him crying out to God, “Let Ishmael live before you!” God said ‘”no” to Ishmael regarding the covenant already set into motion. Still, He promised to bless him and make him fruitful, to multiply him as father of twelve princes and a mighty nation.
Isaac
There was no Isaac in the flesh at the time of this conversation. God, however, foreknew Sarah would bear a son to Abraham whom he would name Isaac. His covenant would be with Isaac, for an everlasting covenant down through his descendants. These things, God had to communicate to Abraham regarding His plan for Sarah, Ishmael and Isaac. Then God finished speaking with Abraham.