Paul certainly knew suffering, and Paul also knew true joy. And he knew joy through suffering. In his darkest hour, he wrote this letter to encourage his most intimate friends. He himself was a prisoner at the time yet it was he who was providing encouragement to them, the faithful at Philippi!
Here is a letter that is pregnant with insights on the real priorities in life, encouragement during difficult trials, and guidance during the inevitable dark times. Inner joy occurs 16 times in these four brief chapters. Paul also deals with some of our thorniest issues: how to deal with Christian troublemakers. He very likely lost his life because of trouble caused by Christians in Rome!
A passage, known among scholars as the Kenosis, teaches of the divinity of Christ, His preexistence, and His equality with the Father.