To understand the "old man" and the "new man," we need to understand the symbolism of water baptism. The apostle Paul describes the process of baptism this way: "Therefore we were buried with Him through baptism into death, that just as Christ was raised from the dead by the glory of the Father, even so we also should walk in newness of life. For if we have been united together in the likeness of His death, certainly we also shall be in the likeness of His resurrection, knowing this, that our old man was crucified with Him, that the body of sin might be done away with, that we should no longer be slaves of sin" (Romans 6:4-6 Romans 6:4-6  Therefore we are buried with him by baptism into death: that like as Christ was raised up from the dead by the glory of the Father, even so we also should walk in newness of life.
 For if we have been planted together in the likeness of his death, we shall be also in the likeness of his resurrection:
 Knowing this, that our old man is crucified with him, that the body of sin might be destroyed, that from now on we should not serve sin.
American King James Version×, emphasis added throughout).
Paul here explains that our water baptism is a symbol of the death and burial of our "old man"—meaning the life we led apart from God. We are further instructed to "put on the new man who is renewed in knowledge according to the image of Him who created him" (Colossians 3:10 Colossians 3:10 And have put on the new man, which is renewed in knowledge after the image of him that created him:
American King James Version×). The new man is our changed Christian lifestyle after baptism, for "as many of you as were baptized into Christ have put on Christ" (Galatians 3:27 Galatians 3:27For as many of you as have been baptized into Christ have put on Christ.
American King James Version×).
After putting to death our old man through repentance and baptism, we put on Christ (by receiving His Holy Spirit through the laying on of hands) to become the new man. At the same time, Paul informs us, "If anyone is in Christ, he is a new creation; old things have passed away; behold, all things have become new" (2 Corinthians 5:17 2 Corinthians 5:17Therefore if any man be in Christ, he is a new creature: old things are passed away; behold, all things are become new.
American King James Version×). When we become a new man, putting on Christ, we also become a new creation. This begins the lifelong process of conversion—becoming like Christ.
The "new man" and "new creation" are the state of a converted Christian after his or her baptism, now striving to always live in accordance with God's way of life.
For more information, please read our booklet Transforming Your Life: The Process of Conversion.