Ephesians elucidates how the Church arrives to full spiritual maturity in Christ. The first part defines the Good News of God's doings (Eph. 1-3). The second sector provides guidelines on how to live in light of those blessings (Eph. 4-5). The book of Ephesians ends with an inspiration to stand firm in the midst of adversity (Eph. 6).
In general from the book of Ephesians, we learn on the power of the Gospel of Christ and how it can break the barriers created by culture.