Axalon,
The biggest problem concerning man is that man thinks this story is all about him. It's not. It's all about a story that God created for His own good pleasure in which man plays his part. The thing is that it is not fiction because all creation is living throughout as actors do on a stage, the world being our stage. The core to the story is about knowing God and Him knowing us by all His promises and His appearing amongst us. There is not one breathing second in all creation that God is not in control of and will not see out until His story is completed.
Now concerning the circumcision of Abraham's family and therefore all Jewish males it was ordained as a sign that those males were under the Covenant made with Abraham. Apart from Abraham's immediate family he had many servants who were to be included in this Covenant so if as suggested that some of them may well have already been circumcised why would they have to be cut again? The thing is though that circumcision did not save for eternal life rather covered one for their earthly existence as Jews. The cutting of the flesh was a sign of the coming Messias carried in Oracle by this people which came to pass by the birth, death and resurrection of Jesus Christ.