The Apostle Paul realized that he was an infant in the faith after his encounter with the Lord Jesus on the road to Damascus. He experienced what was required to become a member of Christ's body and to walk as a mature Christian. Therefore, he wanted to share these truths with the Ephesians and with us.
What does he do? First, he presents doctrine regarding the Holy Spirit, the Lord Jesus Christ, and God the Father. Then, he focuses on the apostles, prophets, evangelists, pastors, and teachers. Why? He knew we needed to acquire knowledge of God's Word and develop a personal relationship with the Triune God.
He concludes this portion of Scripture with comforting words and stern warnings. The former assures us of attaining spiritual maturity, whereas the latter warns against the predators espousing false doctrine, trickery, cunning craftiness, and deceit, which are only overcome by an intimate knowledge of the Son of God.