God initially installs the new man, and it is our responsibility to nourish him. It is clear from various scriptures that he is manifested in our conduct, that he is reconciled to God and man, that he is circumcised of heart, that he is connected with the New Covenant, and finally, that adopting him is a matter of choice on our part.
But, what or who is the new man?
The best way to answer this is to answer yet another question: When does God create the new man in us? Paul answers the question in Galatians 3:27: "For as many of you as were baptized into Christ have put on Christ." He uses the verb enduo, "to put on." Its literal meaning is "to sink into." We sink into Christ when we are baptized. That is when we first clothe ourselves with the new man, or to put it a little bit more accurately, that is when God first establishes him within us.
Paul is clearly describing the new man in Galatians 3:27, and he connects the putting on of Christ with reconciliation. The new man is, by definition, reconciled with God and with man. Paul immediately follows his statement that the baptized person has put on Christ (verse 27) with a statement about reconciliation (verse 28): "There is neither Jew nor Greek, there is neither slave nor free, there is neither male nor female; for you are all one in Christ Jesus." Note the similarity of Paul's terminology and approach with Colossians 3:9-11, where he admonishes us "to put on the new man." Paul also immediately follows this statement with a discussion of reconciliation: "There is neither Greek nor Jew, . . . slave nor free, but Christ is all and in all."
Now we can see how Galatians 3:27 answers these two questions:
1. We put on—sink into—the new man when we are baptized.
2. We put on Christ.
This means Jesus Christ is the new man.
The new man conducts himself according to God's Word, walking according to His law. With this in mind, notice Romans 13:12-14, where Paul tells us how we should walk—we who have put on Christ, the new man: "Therefore let us cast off the works of darkness, and let us put on the armor of light. Let us walk properly, . . . not in revelry and drunkenness, not in licentiousness and lewdness, not in strife and envy. But put on the Lord Jesus Christ."