Old to New (Ephesians 4:17-24)
Paul next calls believers to consciously strive towards a more Christ-like life. Paul speaks elsewhere regarding the "old self" in Romans 6:6 and Colossians 3:9. The "old self" is the old way of life practiced by Christians before their conversion. According to Paul, this "old self" has two characteristics. First, it "belongs" to that previous state, not the current status as a child of God. A believer is not to be associated with the same sinful practices he or she lived for before knowing Christ.
Second, the "old self" is marked by evil brought on by misplaced, deceptive urges. As prior verses indicated, unbelievers, not only "[give] themselves up" to sin, they seem eager to go deeper and further into sin. This is not only damaging to their relationship with God, it's damaging to their lives and physical bodies (Romans 1:27). Sin is deceptive, making us think that what's harmful is what's best for us. The word for "corruption" here in greek is phtheiromenon, which carries the idea of rotting, wasting, rusting, or being defiled. Such things are ruined and useless, with no value to themselves or others. In contrast, believers are called to be like-minded like Jesus and put on the character likeness of Jesus rather than our old selves which brought us death.
Truly understanding saving grace, as Paul explained in prior chapters of Ephesians, the Christian's first motivation for living a godly life. Paul encourages the believers to live in a way that honors that gift. All saved Christians are part of a single, unified family, part of the ''body'' of Christ.