After thirteen years, Abraham was ninety-nine years of age and was becoming old. He considered his own body as being already dead. Even if he wanted to have a son, he could no longer do it. Then God appeared to him and said, "I am the Almighty God" (17:1). This was the first time that God revealed His name as "the Almighty God." The name Almighty God in the original language can be translated as "all-sufficient God." After God revealed this name to him, He put a demand on him. "Walk before me, and be thou perfect." Although Abraham had believed that God is powerful, he might not have believed that God is all-sufficient. This was why he tried to do things by himself. God showed him that if he believed in God as the all-sufficient One, he had to walk before Him as a perfect man. Being perfect is being pure. God required Abraham to be pure and without any mixture.
After God showed this to Abraham, He said, "I will make my covenant between me and thee, and will multiply thee exceedingly...My covenant is with thee, and thou shalt be a father of many nations. Neither shall thy name any more be called Abram, but thy name shall be Abraham; for a father of many nations have I made thee...And I will establish my covenant between me and thee and thy seed after thee in their generations, for an everlasting covenant, to be a God unto thee and to thy seed after thee. And I will give unto thee, and to thy seed after thee, the land wherein thou art a stranger, all the land of Canaan, for an everlasting possession; and I will be their God" (vv. 2-8). God wanted to gain a people through Abraham, and God wanted to be their God.
What kind of a standing should Abraham and God's people take before they can become His people? God said, "This is my covenant, which ye shall keep, between me and you and thy seed after thee; Every man child among you shall be circumcised" (v. 10). In other words, God wants a people, yet they must not have any fleshly activity, power, or strength. Who then are the people of God? They are those who have been circumcised. Circumcision is the mark of God's people. Those who were eight days old, whether they were born in the house or bought with money of any stranger had to be circumcised (v. 12). It was not enough to be born, and it was not enough to be bought. One had to be circumcised as well. We are all born of God and bought by God. As far as redemption is concerned, we were bought by God. As far as life is concerned, we were born of God. But if we are not circumcised, we will have no part in the testimony of the people of God. God told Abraham, "The uncircumcised man child whose flesh of his foreskin is not circumcised, that soul shall be cut off from his people" (v. 14). Those who were not circumcised were to be cut off from among God's people. This has to do with the testimony. It means that those who are not circumcised cannot be vessels for God's testimony. A man may be redeemed and have life, but if he is not circumcised, and if he does not know the flesh-dealing cross, he cannot be of God's people; he still has to be cut off from the people.