What does Ephesians 4:24 mean?

Believers are to put off the "old self" (Ephesians 4:22). Prior verses have explained this as the deceptive, corrupting influence of sin which marks a life of unbelief. Making this change is impossible without Christ (Ephesians 2:8–9), and requires a Christian to be renewed in their thinking by God (Romans 12:2, Colossians 3:10). The contrast to the "old self," and the result of being transformed by Christ, is to "put on the new self."

In Colossians 3:10, Paul notes that "the new self" is being "renewed in knowledge after the image of its creator." In other words, the new self is the life which grows to become more like Christ. This is "created after the likeness of God." Two aspects are noted to explain how the new self is being created as a reflection of the Creator.

First, Paul mentions "true righteousness." This exact phrase is found only here in the New Testament. However, righteousness is a common biblical theme. In Ephesians 6:10–18, Paul will develop the famous "armor of God" analogy, which includes the breastplate of righteousness (Ephesians 6:14). The Lord is righteous and expects His followers to seek to do what is right as well.

Second, the new self is being created like God in "holiness." Believers are to control their bodies "in holiness and honor" (1 Thessalonians 4:4). Holiness is contrasted with impurity (1 Thessalonians 4:7), indicating holiness means to be set apart, clean, and distinct from what surrounds it. Believers are to live holy lives as followers of Christ.