God wants us to grow up (Eph 4:13-16). Children (infants) can be deceived (Eph 4:14, 2Co 11:3). Unity results from knowledge of Jesus Christ. We're to speak the truth in love (Eph 4:15, Eph 5:18-19, Col 3:14-17). When we do we serve the body and the head, Jesus Christ, better.
More than any book Ephesians reveals the blessings from God based on our relationship with Jesus Christ by grace through faith. Eph 1:3 is the a key verse. Other key verses by chapter include Eph 2:8 Eph 3:19 Eph 4:1 Eph 5:18 and Eph 6:10-11.