Why is Ephesians called a prison epistle?
It is called a prison epistle because it was written after Acts 28 while the writer was in prison, along with Philippians and Colossians. These three letters are grouped as prison epistles because they came from that imprisonment period. The term identifies the setting of their composition.
Les explains that Ephesians is one of the prison epistles, or prison letters. After Acts 28, when he is in prison, he writes Ephesians, Philippians, and Colossians. Ephesians is a higher level of doctrine, Philippians a higher level of reproof, and Colossians a higher level of correction. Les also points out that once this jump into higher or deeper spiritual truths is made, there is no longer any mention of a Jew or the Old Testament in these inspired letters; after Acts 28, the turn is to the Gentile.