This teaching comes from chapter 4. It is where Paul shifts, specifically from focusing on practical out-workings in day to day life of the grand vision of the good news about Jesus that he explored in the first half of his letter. In the first half of the letter, he shares this grand vision of Jesus as the redeemer and resurrected king of a new humanity that’s made up of every kind of person ethnically/socioeconomically/culturally. The second half of the letter, he explores what it is actually going to require. The character traits, life habits, moral commitment, and the relational commitment that is going to be required to live as this new and different kind of community together.
Paul wanted these new followers of Jesus to live and become what they really are, adopting new identities.