"Slaves of Christ Jesus"
In the first sentence of the letter, Paul writes:
Paul and Timothy, servants of Christ Jesus. [Philippians 1:1]
The word translated here “servants” is also the word for slaves. (Spelled in English letters, it would be douloi.)
In the status-conscious world of 1st century Greco-Roman culture, to call yourself a servant or slave would seem crazy. And that’s exactly Paul’s point: in Christ, our old ways of gaining status or identifying ourselves have been changed. Paul is therefore proud to be a servant of Christ Jesus, and he wants the Philippians to feel the same way.
Philippians Week 2, Day 1