The fifth of Paul's Epistles, and the tenth book in the New Testament, is Ephesians. It was written some time around 61 AD whilst Paul was a prisoner in Rome, awaiting his trial by the Emperor Nero; a persecutor of Christians.
Paul's letter to the Church at Ephesus (in modern day Turkey) is not an admonishment, like some of his other letters, but rather an encouragement. Paul describes the nature of the Church as a living thing; the body of Christ. He then tells the Ephesians to act like Christ's body on earth.
Ephesians 2:2-6
"wherein in time past ye walked according to the course of this world, according to the prince of the power of the air, the spirit that now worketh in the children of disobedience: among whom also we all had our conversation in times past in the lusts of our flesh, fulfilling the desires of the flesh and of the mind; and were by nature the children of wrath, even as others. But God, who is rich in mercy, for his great love wherewith he loved us, even when we were dead in sins, hath quickened us together with Christ, (by grace ye are saved;) and hath raised us up together, and made us sit together in heavenly places in Christ Jesus"