This section tells us that we are all unified in Christ but are also all different in how the character of Jesus works through us. Jesus, as the victor over His enemies (un-redeemed sinners, like Paul) can now give us gifts in the form of responsibilities and areas of ministry for this new building He is creating.
Christian unity is simply a fact. We are bound together by a common faith, a common life, common purpose and a common loyalty. We serve on Lord and Master, he is the head and we are his limbs (branches) one body of believer, as in 1 Corinthians 12-13. We, however, do not all have the same gifts, talents, temperaments or personalities. What keeps us united as believers is the bond of love. We must continue to mature and grow in Christ so we can all do the will of God for our lives.
The latter half of Chapter 4 forms a single thought going through Chapter 5, verse 5. Essentially Paul is saying to look back when you were an enemy of God—what were your values, attitudes, and actions? Look at it in comparison with who you are now—one “being renewed in the spirit” (vs 23). He wants us to put on a “new self”. This means deliberately discarding the old, selfish way of life, ridding ourselves of former habits and letting the new life change our thinking and remold our patterns of behavior.
With that in mind, he says: “quit acting like you did before you were saved.” Before we knew Jesus, we had no choice but to act in ways not in accordance with His character. Now we have that choice, so Paul says: “act on it!”
All that we think, do and say must be able to withstand God’s searchlight. In a word we are to copy God’s character.