Jesus + Someting Else
Paul is emphasizing the Philippians Church to be Joyful, "rejoice in the Lord", even in all circumstances. Paul is saying that even though I am in prison, I am rejoicing. It shows our great confidence on the God.
Philippians Church is full of Gentile people, but Jewish were saying to them even though you follow Jesus, you have todo circumcision to be saved.
dogs - Trouble makers ( not literal Dogs ), legalists saying that that true spiritual identity (the "true circumcision") comes from human effort or physical rituals instead of worshiping by the Spirit of God.
Grace alone, Faith alone and Christ alone.
Jesus already paid for our sins,