For an introduction to this series, click here.
Paul begins this new section with an important warning against the Judaizers, whose influence would not go away:
"Look out for the dogs, look out for the evildoers, look out for those who mutilate the flesh. For we are the circumcision, who worship by the Spirit of God and glory in Christ Jesus and put no confidence in the flesh" (3:2-3)
I'm sure the Judaizers did not appreciate being called dogs, but that is what Paul calls them. Notice that Paul says the true circumcision, the true followers of God, are those who put no confidence in the flesh.
I don't like to break up a contextual thought, but I did in this case, just so you can better see the introduction Paul gives to this next section:
"Though I myself have reason for confidence in the flesh also. If anyone else thinks he has reason for confidence in the flesh, I have more: circumcised on the eighth day, of the people of Israel, of the tribe of Benjamin, a Hebrew of Hebrews; as to the law, a Pharisee; as to zeal, a persecutor of the church; as to righteousness under the law, blameless. But whatever gain I had, I counted as loss for the sake of Christ. Indeed, I count everything as loss because of the surpassing worth of knowing Christ Jesus my Lord. For his sake I have suffered the loss of all things and count them as rubbish, in order that I may gain Christ and be found in him, not having a righteousness of my own that comes from the law, but that which comes through faith in Christ, the righteousness from God that depends on faith" (3:4-9)
If anybody had Jewish credentials, it was Paul. And he fervently pursued Judaism for many years. But after he gave his life to the Lord, all that was put behind him. Paul's point is that the Philippians need to do the same thing, and not get trapped into following religious dogma trying to please God. A life truly committed to God is always a life of faith: always has been, always will be.
"Not that I have already obtained this or am already perfect, but I press on to make it my own, because Christ Jesus has made me his own. Brothers, I do not consider that I have made it my own. But one thing I do: forgetting what lies behind and straining forward to what lies ahead, I press on toward the goal for the prize of the upward call of God in Christ Jesus. Let those of us who are mature think this way, and if in anything you think otherwise, God will reveal that also to you." (3:12-15, ESV)
Paul took the Christian life seriously, and he tells the Philippians to do the same. We are not on a pleasure cruise here. I know that our vision of our reward in heaven is too small. If we could see this life the way God does, we would take it way more seriously. God has so many good things He wants to do for us and that He has in store for us in heaven, and we get stuck trying to live a "normal" life here. How foolish. C.S. Lewis compared this attitude to a child who wants to keep playing in a mudhole instead of taking the offer to go to the beach.