"Put off the old man, which is corrupt according to the deceitful lusts; and be renewed in the spirit of your mind; and put on the new man, which after God is created in righteousness and true holiness."
After we become believers in Christ we are commanded to throw off our old nature or "old man" which is namely our pride, covetousness, lasciviousness, unrighteousness, wrath, enmity, hatred, etc.; all of which must die in the wise believer, if ever our new nature or "new man" shall arise, which is day by day renewed in the Spirit. For as believers in Christ we must remember:
"Ye are not your own; for ye are bought with a price; therefore, glorify God in your body and in your spirit, which are God's."
1 Cor. 6:19, 20
In proportion as our old nature dies, our new nature is quickened in the Spirit. As our pride loses its influence, humility, by the grace of God in the Holy Spirit, succeeds; as anger yields, meekness advances; as covetousness is done away, trust in God's Word is increased; and as the love of the world disappears and is removed, the love of Christ takes its place in our soul. In this process consists the renovation of the new nature. and is the fruit of the Spirit. This is the Word living in us, being written on our hearts; this is the new man of Christ, the result of the new birth in us, in which we must live if we are to be true children of the living God.
"I will put my law in their inward parts, and write it in their hearts; and will be their God, and they shall be my people." Jer 31:33
Let the true follower of Christ who denies himself, and a false Christian who is filled with inordinate self-love, be compared together. If an insult be offered to the latter, you may soon see his temper rising, and visible marks of anger; and these are, not unfrequently, followed up by spiteful language and actions, by a spirit of revenge, and imprecations with curses. All this proceeds from the old nature, whose proper character it is to be angry and bitter, and to exhibit prideful superiority. On the contrary, he that is a true follower of Christ has sincerely begun to practice self-denial, is gentle, patient, and ready to forgive; free from a revengeful spirit; full of compassion and tenderness; and esteems himself worthy of all the sufferings which the will of God may be pleased to allot to him. These qualities are all included in putting off the old nature of the flesh and walking in the Spirit.
Our Saviour has set us an example by willingly denying himself. "The Son of man," he says, "came not to be ministered unto, but to minister" (Matt. 20:28); and again, "I am among you as he that serveth" (Luke 22:27); and in another place, "The Son of man hath not where to lay his head." Luke 9:58. David, when reviled by Shimei, practiced the duty of self-denial, for his words were: "The Lord hath said unto him, Curse David." 2 Sam. 16:10. As if he had said: "I am a worm in the sight of God, and deserve to suffer far worse things." And thus have all the saints and prophets of God freely denied their own will, and esteemed themselves unworthy of every blessing. They bore the burden of their day with patience (Acts 5:40, 41); they cursed not when they were cursed; and prayed for them by whom they were slaughtered (Acts 7:60); and thus, "through much tribulation, entered into the kingdom of God." Acts 14:22.
Now, this self-denial is the cross of Christ, which he has encouraged us to bear, saying:
"If any man will come after me, let him deny himself and take up his cross daily, and follow me." Luke 9:23
This self-denying life is a severe cross to the flesh; the natural man desires a life free from restraint and Godly command. The "old man" nature would rather follow the inclination of his own will, and seek after his own ease and pleasure in complete disregard to others; rather than serving in the humility, patience, and meekness of Christ, following the teachings of Christ's life and example.