"Mortify therefore your members which are upon the earth; fornication, uncleanness, inordinate affection, evil concupiscence, and covetousness, which is idolatry: for which things' sake the wrath of God cometh on the children of disobedience: in the which ye also walked sometime, when ye lived in them. But now ye also put off all these; anger, wrath, malice, blasphemy, filthy communication out of your mouth. Lie not one to another, seeing that ye have put off the old man with his deeds; and have put on the new man, which is renewed in knowledge after the image of Him that created him: where there is neither Greek nor Jew, circumcision nor uncircumcision, Barbarian, Scythian, bond nor free: but Christ is all, and in all." Colossians 3:5-11
"Mortify therefore your members which are upon the earth ... seeing that ye have put off the old man with his deeds; and have put on the new man, which is renewed in knowledge after the image of Him that created him."
Since Christians are joined to Christ Jesus in His death and resurrection -- their sins and sinful nature having been crucified with Christ. And, having been raised up with Christ by the mighty working of God's Spirit to a new life in fellowship with the LORD God, they are to put to death (to mortify) their sinful nature with all its desires and put on the new man which is created by the Holy Spirit and seeks to be like Christ.
Christians in this world have two natures, called in the Bible the old man (inherited from sinful Adam) and the new man (created in them by the regenerating work of God's Holy Spirit). In the beginning, man's nature was single and united in love for God, trust in Him and the desire to honor and glorify His holy name, for the first man and woman were created in the image of God and knew Him and His will and desired to live for Him (Gen. 1:26-27). But, when Adam and Eve fell into sin, that nature was lost, for they doubted God's Word, were afraid of God and even tried to hide from His presence (Genesis 3). A reading of the pages of the Bible which follow the fall reveals the sinfulness and depravity of mankind.
Those who have been raised up from spiritual death and darkness to faith in Christ Jesus -- whether it was the Messiah yet to come in Old Testament times or, as it is now, the Christ who has come and accomplished mankind's redemption -- have a new nature which loves the LORD God, trusts in Him for salvation and all things and desires to live for Him and serve Him. But, as long as Christians are yet in this world, they have, as well, their old sinful nature, inherited from Adam.
Thus, the Christian life is a life of struggle, not only with the world without but with the sinful nature within. Christians, thankful for the shed blood of Jesus and the blessings of forgiveness and life eternal He has won for them, love God and want to live for Him in accord with His Word. Yet, there remains within them a nature which loves self, doubts the Word of God and would rather go its own way and seek its own glory and pleasure.
St. Paul writes of this internal struggle to the believers in Rome: "For I know that in me (that is, in my flesh,) dwelleth no good thing: for to will is present with me; but how to perform that which is good I find not. For the good that I would I do not: but the evil which I would not, that I do. ... For I delight in the law of God after the inward man: but I see another law in my members, warring against the law of my mind, and bringing me into captivity to the law of sin which is in my members" (Rom. 7:18-19, 22-23).
This is why Christians rejoice in the fact of God's continuing forgiveness for sins and shortcomings. They continually acknowledge their sins and trust that God is merciful to them and forgives them for the sake of Jesus and His blood shed upon the cross for the sins of the world. Christians do not deny or cover up their sinfulness, but walk in the light, trusting that "the blood of Jesus Christ His Son cleanseth [them] from all sin." They agree with God and confess their sins, trusting that He is faithful and just to forgive their sins and cleanse them from all unrighteousness for the sake of His Son, Jesus Christ the righteous, who is the propitiation -- the atoning sacrifice -- for the sins of all people (cf. 1 John 1:5 -- 2:2).
It is also why believers look forward to the day of Christ's return, for then the image of Christ will be perfectly restored in them -- they will no longer be subject to sin and their old sinful nature. The Bible says: "Our conversation is in heaven; from whence also we look for the Saviour, the Lord Jesus Christ: who shall change our vile body, that it may be fashioned like unto His glorious body, according to the working whereby He is able even to subdue all things unto Himself" (Phil. 3:20-21); "We know that, when He shall appear, we shall be like Him; for we shall see Him as He is" (1 John 3:2).
And so, while believers in Christ await His glorious return and the redemption of their bodies (cf. Rom. 8:23), they put to death the old man and all that is contrary to God's Word and put on the new man which gladly and willingly seeks to live as God commands. They agree with God's Word that such things as fornication, uncleanness, inordinate affection, evil concupiscence, covetousness, anger, wrath, malice, blasphemy, filthy communication and lying are wrong; and they acknowledge their sins and failures, trusting in Christ's shed blood for forgiveness, and then seek God's help and strength to live for Him in accord with His Word.
The battle is not easy, for the old sinful nature and inclination is strong and is encouraged and incited by the devil and the sinful world in which Christians live. No matter how hard people try, they cannot drive out the darkness of sin from their lives. But Christians, by the grace of God, turn to Christ Jesus, the Light of the world. He cleanses them of all sin with His own holy and precious blood, and He strengthens and keeps them in the true and right way unto life everlasting!
O Lord and Savior Jesus Christ, for the sake of Your blood, shed for me upon the cross, forgive me for my utter sinfulness and for my many shortcomings and transgressions in regard to Your holy commandments. Fill me with Your Spirit, give me the desire to walk in Your ways, and keep me in the true and saving faith unto life everlasting. Amen.
[Devotion by Randy Moll. Scripture quoted from the King James Version of the Bible.]