Circumcision in the Old Testament is the equivalent of baptism in the New Testament (Col. 2:11-12). Both baptism and circumcision have the same purpose—to terminate our natural being and bring us into resurrection. Why are we baptized after believing in the Lord Jesus? Because we realize that our old man has been crucified with Him and that we must be buried so that we may be one with Him in His resurrection. Hence, Abraham's circumcision has the same significance as our baptism. In both circumcision and baptism the principle is the same. Although Abraham was justified in Genesis 15, he was circumcised in Genesis 17. As circumcision was the sign of Abraham's being justified, so baptism is the mark of our being saved. How can we prove that we have been saved? By living a life of baptism, a life of one who has been crucified, buried, and resurrected. If we live such a life, everyone will be able to see upon us the mark of our salvation.
Circumcision corresponds to the changing of human names (17:5-6, 15-16). As we have seen, to change the name is to change the person. When Abraham's name was changed, his person was changed also. This was especially true of Jacob. When Jacob's name was changed to Israel, his person was changed (32:27-28). This change of name can only be accomplished through circumcision, through having ourselves terminated and ushered into resurrection. Then we are no longer a natural person but a resurrected person. Being terminated and ushered into resurrection is the real changing of a person. Hence, circumcision corresponds to the changing of names. Now we can understand why the changing of names and circumcision are both revealed in the same chapter. These two things are actually one. The changing of names and circumcision both mean to terminate our old being and to bring us into resurrection so that we may be another person.
Romans 2:28-29 says that circumcision is not "outward in the flesh," but "of the heart, in the spirit, not in the letter." Circumcision is not an outward matter; it is an inward one (Phil. 3:3). The same is true of baptism. Baptism should not just be a form; it must be an inward reality. Let me tell you a story that I heard more than forty years ago. In Central America, the Catholic Church accepted and baptized as members many people who were not saved. One day, a certain priest sprinkled a few drops of water on a boy's head and changed his name to John. At that time, the Catholic Church insisted that on Fridays its people eat only fish, not meat. One Friday, this John had only meat to eat. Since the priest had sprinkled water on his head and had changed his name to John, he thought that he could do the same to the meat. Therefore, he sprinkled water on it and called the meat fish. He then proceeded to cook the meat by boiling it. As he was boiling the meat, the priest came by. Smelling the aroma of boiling meat, he was angry with John and asked him what he was doing. John replied, "I am doing nothing wrong. This is not meat; it is fish. Don't you remember sprinkling water on me and changing my name to John? I followed your way and sprinkled water on the meat and called it fish." This is not real baptism nor the genuine changing of names. Baptism must be an inward reality in the spirit, not an outward form of sprinkling a few drops of water on a person's head.