Ephesians 4:17-24

v17-21: "Converted Gentiles must not live like unconverted Gentiles."  At one time we were devoid of all saving knowledge and ignorant of many things about God "because we wanted to be so."  Preferring the darkness to the light and having "a dislike and aversion to a life of holiness," we made it our "common practice to commit all kinds of immorality."  But not anymore.  When we came to know Christ, we were "saved from the darkness and defilement" and are now "obliged to lead better lives."

v22-24: Our old self, "this corrupt nature innate in us," inherited from Adam and which we brought into the world with us must be taken off and put to death, and the new self must be put on.  The new self enables a person to live a new life, the life of righteousness toward people and holiness toward God they are required to live.