"But ye have not so learned Christ; if so be that ye have heard him, and have been taught by him, as the truth is in Jesus: that ye put off concerning the former conversation the old man, which is corrupt according to the deceitful lusts; and be renewed in the spirit of your mind; and that ye put on the new man, which after God is created in righteousness and true holiness." (Ephesians 4:20-24)
The "old man" is the believer's former STATE of guilt and condemnation. The "new man" is the believer's present STATE in Christ, justified, sanctified, qualified, in God's eternal favor and fellowship, and entitled to all of salvation based on the righteousness of Christ freely imputed and received by faith. We did not gradually in degrees become the "old man" in Adam. We were born that way and started out that way before we committed the first sin in our character and conduct. As saved sinners we do not gradually in degrees become the "new man" in Christ. We are born again that way and start out that way before we perform the first act of obedience in our character and conduct. "Old man" and "new man" are states.
To "put off concerning the former conversation the old man" is to remind ourselves continually that we are no longer in a state of wrath. Putting on "the new man" is to remind ourselves continually that we who are submitted to Christ's righteousness are in an eternal, unchangeable state of salvation. This new man, this state before God, is the fruit and result of the righteousness and holiness of Christ, which will result in our character and conduct being perfectly conformed to Christ's image in Heaven.
"Corrupt according to the deceitful lusts" has to do with unlawful desires which are "deceitful." Unlawful desires of immorality are not "deceitful" even to lost men. These unlawful desires which deceived "the old man" have to do with legalism, not being submitted to the righteousness of Christ. These unlawful desires are the same thing as fruit unto death the attempts of guilty, condemned sinners to establish their own righteousness before God. This is an evidence of the old man!
The apostle goes on to say that because we who believe God's gospel are already in a state of perfect blessedness, secure in Christ, fully entitled to all of salvation, sure to be perfectly conformed to Christ's image in Heaven, let us diligent in obedience without legalism. Let our conformity to Christ begin in this life. Let us, as those who have put off the old man and have put on the new man, seek to love God and to love our neighbor as ourselves. This is honoring and pleasing unto God.