What is the main idea of the book of Ephesians?

Your study bible will probably tell you it is about God's divine purpose and grace...This is helpful but I think it is even more simple. Ephesians is basically a concise gospel presentation followed by instructions on how you should respond to this message... Therefore the main idea of Ephesians is: God has brought you from death to life through Jesus, therefore you're response should be x,y,z...