"'I will make you very fruitful; I will make nations of you, and kings will come from you. I will establish my covenant as an everlasting covenant between me and you and your descendants after you for the generations to come, to be your God and the God of your descendants after you. The whole land of Canaan, where you are now an alien, I will give as an everlasting possession to you and your descendants after you; and I will be their God.'" NIV translation
God gives his obligations and promises as part of the adoption contract. He renewed the promise of children and also the possession of the land of Canaan. This land is the country of Israel today and even though there is much arguing about who owns the land, we can say that all of it belongs to Israel. We should take note that God said it was their "everlasting" land and so cannot be given or taken away by any man.
"Then God said to Abraham, 'As for you, you must keep my covenant, you and your descendants after you for the generations to come. This is my covenant with you and your descendants after you, the covenant you are to keep: Every male among you shall be circumcised.You are to undergo circumcision, and it will be the sign of the covenant between me and you.'" NIV translation
Every contract has rights and responsibilities and now God lays out Abraham's responsibility. This contract was to be binding on all of his descendants and they were all to be circumcised. This physical sign was a picture of the coming circumcision of the heart.
"'For the generations to come every male among you who is eight days old must be circumcised, including those born in your household or bought with money from a foreigner - those who are not your offspring. Whether born in your household or bought with your money, they must be circumcised. My covenant in your flesh is to be an everlasting covenant. Any uncircumcised male, who has not been circumcised in the flesh, will be cut off from his people; he has broken my covenant.'" NIV translation
We see a picture of what is known as "the age of accountability" in the fact that boys were not required to be circumcised until they were eight days old. Throughout the Bible, the number eight is associated with resurrection and a new creation. This is a reminder that, with the circumcision, the males were being set apart and marked as God's people. This physical circumcision marking was a shadow of the mark that we have through the Holy Spirit as Christians. We also see that this covenant was made available to Gentiles who were purchased by Abraham and his descendants. This was a stumbling block for the early church as they did not understand that Jesus came for the Gentiles as well as the Jews and it was pictured in the covenant of circumcision. Finally, we see that the punishment for not going through with the act of circumcision was that they were to be cut off (separated) from their people. In the same way, those who reject the circumcision of the heart through Jesus Christ, will be separated from God for all eternity. God is just in this because they have broken the terms of the contract.