Paul reminds the Philippians about his life without Christ and about his life in Christ to safeguard them from those who would pervert the Gospel.
“1 Further, my brothers and sisters, rejoice in the Lord! It is no trouble for me to write the same things to you again, and it is a safeguard for you. 2 Watch out for those dogs, those evildoers, those mutilators of the flesh. 3 For it is we who are the circumcision, we who serve God by his Spirit, who boast in Christ Jesus, and who put no confidence in the flesh—4 though I myself have reasons for such confidence. If someone else thinks they have reasons to put confidence in the flesh, I have more: 5 circumcised on the eighth day, of the people of Israel, of the tribe of Benjamin, a Hebrew of Hebrews; in regard to the law, a Pharisee; 6 as for zeal, persecuting the church; as for righteousness based on the law, faultless. 7 But whatever were gains to me I now consider loss for the sake of Christ. 8 What is more, I consider everything a loss because of the surpassing worth of knowing Christ Jesus my Lord, for whose sake I have lost all things. I consider them garbage, that I may gain Christ 9 and be found in him, not having a righteousness of my own that comes from the law, but that which is through faith in Christ—the righteousness that comes from God on the basis of faith. 10 I want to know Christ—yes, to know the power of his resurrection and participation in his sufferings, becoming like him in his death, 11 and so, somehow, attaining to the resurrection from the dead.”
— Philippians 3:1-11