This passage describes a simple truth regarding overcoming sinful behavior. Knowing Jesus Christ allows us to put away our old, sinful ways by replacing them with new, righteous ways. You can’t do one without the other. Notice the contrasting phrases: Put off the old, and put on the new. Do not nurse your anger, but resolve it quickly. Don’t steal, but work and be generous. What do you need to put off and put on to live in a way that glorifies God, loves others, and wins them to faith in Jesus Christ?
But that is not the way you learned Christ!—21 assuming that you have heard about him and were taught in him, as the truth is in Jesus, 22 to put off your old self, which belongs to your former manner of life and is corrupt through deceitful desires, 23 and to be renewed in the spirit of your minds, 24 and to put on the new self, created after the likeness of God in true righteousness and holiness. 25 Therefore, having put away falsehood, let each one of you speak the truth with his neighbor, for we are members one of another. 26 Be angry and do not sin; do not let the sun go down on your anger, 27 and give no opportunity to the devil. 28 Let the thief no longer steal, but rather let him labor, doing honest work with his own hands, so that he may have something to share with anyone in need.—Ephesians 4:21-28, ESV
John Newton was a British Slave trader who became a Christian and fought for the abolition of slavery.