Paul ended his letter to the Philippians where he started. At the beginning of the letter, he told them he was a prisoner in a Roman jail. But that worked for his spiritual advantage because he was able to witness to those who belonged to Caesar's household. He thought that was a wonderfully strategic advantage. Now we see that some of Caesar's house became Christians! And those Christians sent greetings to the Christians in Philippi. What a marvelous thing. Paul built a church around him in jail. Those who became believers through his witness wanted other Christians to know about them and be greeted by them.
22 All the saints greet you, especially those of Caesar's household.
23 The grace of the Lord Jesus Christ be with your spirit. (Phil 4:22-23)
For Paul, life was a place of strategic and tactical advantage. Always he looked for ways to advance the kingdom of Christ. His value system was built around people and their spiritual advantage. What made him happy was the happiness of others as they discovered the beauty of Jesus Christ, and the love of God the Father, and the power of the Holy Spirit. That kind of happiness no one can take away.