The Sign of the Covenant

Thirteen years after the birth of Ishmael, God reiterates His blessings and covenant with Abram. God gives Abram a sign of the covenant to be from now on: circumcision. God changes their names to Abraham and Sarah. They both laugh when they are told of the child to be born to them in their old age, and God makes it clear that nothing is too hard for Him. Though Abraham initially laughed, he obeys God's command and circumcises all in his household that same day. Is our obedience that complete and immediate?