Lets do some background reading about the beginnings of the Ephesian Church. Acts 18-20 take place approximately in the early to mid 50's AD.
Paul wrote the letter to the Ephesians while in prison in Rome around 60 AD.
Then in the mid 80's AD, John writes about the Ephesian church in the book of Revelation.
So we are able to get a 30 year look at the progress and regress of the church in Ephesus. How does this help you understand the book of Ephesians? Are you getting some clues as to why Paul would choose to write what he does?
Discipleship & Ephesians: In Ephesians 2, Paul teaches that we were dead but Christ has made us alive. The implication is that we were dead because of how we lived. When Christ made us ALIVE we lived differently. This is the life of discipleship. Check out this article on why discipleship and christianity can never be separated.