Paul writes the Ephesian believers so they include Gentile believers but not practice sinful Gentile traditions, imprisoned under Gentile authority he instructs them to follow all authorities for sake of the gospel , this is God's plan, his imprisonment is furthering the gospel.
Paul writes to Colossian believers and warns them against Jewish legalist who keep the Law for righteousness, he tells them their righteousness is in Christ and to live Holy for the sake of the gospel.