When Paul exhorts us not to “put confidence in the flesh” he’s referring to human achievement. When we base our worth on our accomplishments we are building our lives on a faulty foundation. No one knew that any 
better than Paul did. He had built his whole self-image and self-worth on his ancestry and religious accomplishments. In Philippians 3:4-6 Paul describes them. He writes, “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.”
Paul points out seven things he used to put his confidence in. The first four of them are things that associated him with God’s people. He was circumcised at the right time. This had become an area of pride among Jews who lived in Gentile territories. His second point however acknowledges that many Gentiles converted to Judaism and were circumcised also so he says he was not a proselyte to Judaism, but of the very physical lineage. Third, not only from Jewish blood but traceable to the tribe of Benjamin. Fourth not only all this but even though born outside of the Promised Land in Gentile culture he spoke the biblical language of Hebrew, thus he was a Hebrew of Hebrews. None of the Judaizers who were promoting a false gospel had such credentials. If there was anyone to listen to regarding Judaism and its relationship with Christ, it should have been Paul.
These four inherited traits were them followed by three personal accomplishments. Regarding the law itself no one studied it more or knew it better than the Pharisees! Paul was one of them. Hughes comments that, “Paul was a brilliant, intransigent Pharisee, a heavyweight who could hold his own with anyone.” Second, he was a persecutor of the church. He led campaigns to stamp out the new sect of Christianity in its early days. This history should lead his Jewish brothers to give weight to his testimony about Christ. Finally, Paul claimed to be “blameless” under the law. It wasn’t perfect, but it was an exemplary Jewish life which was above reproach. If anyone had the right to boast in Jewish heritage, knowledge, conviction, or performance it was Paul. But Paul is going to explain how no religious heritage or association can win God’s favor. He’s going to explain how nothing but the blood of Christ is sufficient to make us acceptable to God. Everything else is meaningless! What am I putting my confidence in? What’s in your wallet?