God, who called the world into existence and who called Abram to follow him, reaches his hand into the history of the world and renames Abram to Abraham in Genesis 17. This isn't just a nickname from a coach or family member; God's naming power is a revealing of a new reality in the life of Abraham.
The promises that come to Abraham cover three areas: a multitude of descendents, a convenant with God, and the land for future generations. You might expect that Abraham, a man of faith, would be eager to embrace these promises, but in fact he hesitates. It isn't the receiving of land that he has a problem with. It isn't even the announcement that the covenant would require all the men to be circumcised. Instead he laughs at God when the promise of a son through Sarah comes.
Perhaps Abraham was worried that he wasn't the spry 86 year old he was when Ishmael was born, or maybe he couldn't imagine Sarah pregnant, even through a miracle. Whatever the case, Abraham asks God if he can do a substitute in the plan. He asks to make Ishmael a great nation, and God agrees. Ultimately, we see enmity develop between the generations of these two sons of Abraham.
How easy it is for us to feel wise in our own eyes and to substitute our own plans for those of God. Let us be people with minds open to the miraculous ways God can work, and trust Him to get the details right.