Philippians 3:3-4a

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--though I myself have reasons for such confidence.

For it is we who are the circumcision 
Romans 2:28-29  A person is not a Jew who is one only outwardly, nor is circumcision merely outward and physical. No, a person is a Jew who is one inwardly; and circumcision is circumcision of the heart, by the Spirit, not by the written code. Such a person's praise is not from other people, but from God. 
Galatians 6:15  Neither circumcision nor uncircumcision mean anything; what counts is the new creation.
Colossians 2:11-12  In him you were also circumcised with a circumcision not performed by human hands. Your whole self ruled by the flesh was put off when you were circumcised by Christ, having been buried with him in baptism, in which you were also raised with him through your faith in the working of God, who raised him from the dead.

who boast in Christ Jesus, and who put no confidence in the flesh 
Romans 15:17  Therefore I glory in Christ Jesus in my service to God.
Galatians 6:14  May I never boast except in the cross of our Lord Jesus Christ, through which the world has been crucified to me and I to the world.

though I myself have reasons for such confidence 
2 Corinthians 11:21-16  Whatever anyone else dares to boast about--I am speaking as a fool--I also dare to boast about. Are they Hebrews? So am I. Are they Israelites? So am I. Are they Abraham's descendants? So am I. Are they servants of Christ? (I am out of my mind to talk like this.) I am more. I have worked much harder, been in prison more frequently, been flogged more severely, and been exposed to death again and again. Five times I received from the Jews the forty lashes minus one. Three times I was beaten with rods, once I was pelted with stones, three times I was shipwrecked, I spent a night and a day in the open sea. I have been constantly on the move. I have been in danger from rivers, in danger from bandits, in danger from my fellow Jews, in danger from Gentiles; in danger in the city, in danger in the country, in danger at sea; and in danger from false believers.

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