Why are Ephesians, Philippians, Colossians, and Philemon called the prison epistles?
Paul wrote these letters while imprisoned in Rome, shortly before he was martyred. That circumstance is why they are commonly called the prison epistles. They are also distinguished as church epistles, with no mention of the Old Testament or Jew, because all has flowed into the Body of Christ.
Les explains that Ephesians, Philippians, Colossians, and Philemon are normally referred to as the prison epistles because they were written while Paul was in prison in Rome, shortly before he was martyred. He further notes that in these prison epistles there is no single mention of the Old Testament and not a reference to the Jew, because everything has now flowed into the teaching of the Body of Christ, in which there is no distinction—no Jew and no Gentile so far as a division of background. All have become one as members of the Body of Christ. Les says this is strictly church ground, profoundly directed to the position of the church age believer, and not found in the Old Testament, the four Gospels, Acts, or even Paul's letters of Romans and Corinthians. He also mentions that ninety-some times in just six chapters the prepositional phrase “in Him,” “in Christ,” or “in Whom” depicts our position.