The believer who would be truly spiritual must recognize the presence of the old sin nature that remains in his flesh body even after their salvation experience. All one has to do is monitor their thoughts and acknowledge the awful things we think even if we never act upon them...thoughts of hate, temptations considered, anger, manipulation, self-seeking, etc. It would be dangerous not to recognize a foe so near as being in our flesh bodies "members" (Rom 7:17-23).

The old sin nature in the believer is that which is "begotten of (in) the flesh (body)." This sinful nature is called, "the flesh," "the old man," "the natural man," "the carnal mind," "sin in the flesh (Rom 8:3b)." We are not to heed or live by the impulses of our "flesh."

Just as "they that are in the flesh cannot please God" (Rom. 8:8) so that which is of the flesh or is prompted by the flesh, cannot please God. Even flesh inspired religious works cannot please God. God is only pleased by the works occurring "of Christ" (cf., 2Cor 3:3, 10:5) moving within and through the believer according to His will.

"The flesh," as we have already seen, is totally depraved. God calls it "sinful flesh" (Rom. 8:3), warns that it seeks "occasion" to do wrong (Gal. 5:13), and declares that "the works of the flesh" are all bad (Gal. 5: 19-21).

The old nature in the believer will never improve by its contact with the new nature that is by Christ Spirit indwelling that our human spirit where we are "one with" Him (1Cor 6:17). It is with respect to "the flesh" in the believer, even in himself that the Apostle Paul declares that in it "dwelleth no good thing" (Rom. 7:18), that it is "carnal, sold under sin" (Rom. 7:14), that it is "corrupt according to the deceitful lusts" (Eph. 4:22), that it is at "enmity against God," and is "not subject to the law of God, neither indeed can be" (Rom. 8:7).

"The flesh," even as it remains in the believer after salvation, is that which was generated by a fallen begetter... "the Serpent" in the Garden of Eden. The flesh sin-nature  is the old Adamic nature that came into the world by Adam's fall. It is sinful in itself. It cannot be improved. It cannot be changed. Jesus said; "That which is born [begotten] of the flesh is flesh," (John 3:6). It is as impossible to improve the "old man" in the believer as it was to make him acceptable to God in the first place. It took Christ to make us acceptable and only He could divorce us from our flesh, and only the power of Chris tin us can proceed to make us renewed in our soul.

The "old man" was condemned and dealt with judicially at the Cross. Here below Paul says we died with Christ so that our sinful body in which we dwell can no longer have dominion over us.

"We know that our old (unrenewed) self was nailed to the cross with Him in order that [our] body [which is the instrument] of sin might be made ineffective and inactive for evil, that we might no longer be the slaves of sin. (Romans 6:6 (AMP)

Paul then says we are to live by our new life, which is by the Sprit of life in Christ who indwells us as our new life.

"I have been crucified with Christ [in Him I have shared His crucifixion]; (now) it is no longer I who live, but Christ (the Messiah) lives in me; and the life I now live in the body I live by faith (faithfulness) of the Son of God, Who loved me and gave Himself up for me. (Gal 2:20 (AMP)

Never once is the believer instructed to try to do anything with him or to make anything of him or to improve him... but always to "reckon" him "dead indeed" (Rom. 6:11), and to "put him off" (Col. 3:8-10).