so that it has become known throughout the whole imperial guard and to all the rest that my imprisonment is for Christ.All that has happened to Paul has really served to advance the Gospel (Philippians 1:12), and now he tells us exactly how the gospel has been advanced.
(Philippians 1:13, ESV)
Most believe that Paul is in prison in Rome when he is writing this letter to the Philippians. The way that he states that the Gospel has been advanced, supports this idea. The word that is translated "imperial guard" is the Praetorian, or Caesar's Guard. So, whether by direct contact or by word of mouth, there are many in Rome who know that Paul's imprisonment is for Christ.