"If indeed you have heard Him and have been taught by Him, as the truth is in Jesus: that you put off, concerning your former conduct, the old man which grows corrupt according to the deceitful lusts, and be renewed in the spirit of your mind, and that you put on the new man which was created according to God, in true righteousness and holiness. Therefore, putting away lying, Let each one of you speak truth with his neighbor, for we are members of one another. Be angry, and do not sin: do not let the sun go down on your wrath, nor give place to the devil. Let him who stole steal no longer, but rather let him labor, working with his hands what is good, that he may have something to give him who has need. Let no corrupt word proceed out of your mouth, but what is good for necessary edification, that it may impart grace to the hearers. And do not grieve the Holy Spirit of God, by whom you were sealed for the day of redemption. Let all bitterness, wrath, anger, clamor, and evil speaking be put away from you, with all malice. And be kind to one another, tenderhearted, forgiving one another, even as God in Christ forgave you." -Ephesians 4:21-32
In this passage, we have perhaps the most all-encompassing concept in Christianity- putting off the old man and putting on the new man. These terms refer to a person's nature before coming to Christ (the old man) and after being saved (new man). This idea is so huge because it is all-encompassing: it spans our words, thoughts, actions, relationships, and overall lifestyles. It can't be limited to only one or a few areas of our lives. This is also not optional. It is not only for "uber-Christians" who are completely given over to the Lord. Putting off the old man and putting on the new man is cumpulsory to any true believer. Putting off the old man requires removing from our lives anything that had to do with our old sin nature- lying, grudges, hatred, lust, selfishness, etc. Putting on the new man entails doing what is right- loving one another, uplifting and edifying others, sharing God's Word, etc. Any true believer's walk with the Lord will have both of these things.
The most important thing is to make sure that we are BOTH putting off the old man AND putting on the new man. Not only are we to stop lying, but we must also share the truth of Christ with others. It is not sufficient to mearly begin to use our words for righteousness. We must at the same time stop using our mouths for unrighteousness. We cannot begin to forgive and be kind until we are putting off wrath and malice. Neither one of these is optional. God is not pleased with the man who puts off the old man but fails to put on the new, nor is he satisfied with one who puts on the new but fails to cast off the old. There are many dangers to doing one without the other, so it is imperative that we do both.
If we put off the old man without putting on the new man, we are not truly changed and become susceptible to falling back to our old nature again. Jesus illustrates this point in Matthew 12:43-45, comparing such a person to a man who has a demon cast out of him, but since he does not fill the new vacancy in his life with Christ, he ends up having seven demons enter him and is worse off than before. Think of a military general who has just conquered some new land. Does he then leave and hope that the army he just defeated does not try and reclaim the land? Of course not! He will naturally try to fortify his new possession and try to keep his newly conquered grounds. It is the same way in our lives. If we are able to overcome a sin in our lives, we run the danger of allowing that sin to come back unless Christ enters the new vacancy in our lives that the sin used to inhabit. If you used to struggle with stealing, instead use your hands to give to others. If your mouth used to be vulgar, instead use your words to bless others.
There is just as great a danger in attempting to put on the new man without putting off the old. Trying to live this way is hypocritical and discredits your Christian witness. James said it best in James 3:10 when he said, "Out of the same mouth proceed blessing and cursing. My brethren, these things ought not to be so." He compares such a mouth to a fountain which brings forth both fresh water and bitter water. We all know that if there is any bitter water in a cup of water, the whole thing is bad. Such a Christianity makes a no different from the world, for many sinners also do "good" deeds, but that can't undo sin. Many give the excuse that we are "saved by grace" or that "nobody's perfect" but that is not a Christ-like way of thinking. We cannot truly worship God and still have bitterness or wrath inside of us. Such hypocrisy was the sin of the Pharisees, who would do all the right things but still sin and miss the bigger picture.
Sadly, we all know both kinds of people. Some people try not to do the wrong thing either out of fear of consequence or in order to fit in, but they do not put on the new man and try to live like Christ at all. Others try to serve two masters by doing whats right and serving Christ sometimes, but also living after the flesh in a worldly manner. Such people are half-hearted, lukewarm, two-faced, and hypocritical. This is not the type of Christianity that God wants or asks of us. It is time for you and me to put off the old man AND put on the new man. This can look many different ways. Are you influenced by your friends to sin? Flee temptation and influence them for Christ. Do you use your hands to hurt others? Stop, but also use your hands to give to others and serve others. Do you frequently discourage and make fun of people with your mouth? Cease doing that, and instead encourage others in the Lord. Do you have an obsession that consumes your time? Do not simply try and defeat the obsession, but use your newly freed up time to read the Word, pray, or share the Gospel. There are a million different ways to do this. What is important is that you do it, and do it thoroughly. Put off the old man and put on the new man. Don't settle for anything less.