In Genesis 17, Abram’s name is changed to Abraham because
I have made you a father of many nations
God makes a promise to Abraham, promising a land and a people. Multiple peoples, in fact. God also introduces circumcision, to be a sign of the covenant made between God and Abraham. So if you’ve ever wondered why circumcision was initially conceived of, now you know!
God also promises Abraham a son by his wife Sarai (who’s name is now changed to Sarah). Abraham is of course astounded that he would have a son born whilst he himself is 100. Wouldn’t you be? :P
God also promises good things for Ishmael and the generations following him.
All I know is I wouldn’t want to be anywhere near Abraham’s camp that night… lots of circumcision going on :/ Not such a great night to be a male in Abraham’s household, though it was the sign of a great promise :)