The Judaizers thought that they had reason to boast of their success obeying the commands of the Mosaic law, using it to make a claim upon God for their salvation, but Paul had an even greater basis for such boasting, as Philippians 3:4–6 explains. He lived a blameless — not sinless — life according to the Mosaic stipulations. Moreover, he was born into the tribe of Benjamin, the only Israelite clan besides Judah to remain loyal to the Davidic monarchy (2 Chron. 15:1–2; Ezra 4:1). Finally, his dedication to the Law was so great that he made the Law his chief end, persecuting other Jews who, in the name of their Messiah, did not force Gentiles to conform to the law of Moses (Acts 8:1–3; 9:1–2). That is, he persecuted the early church.
Prior to meeting Christ on the Damascus Road, Paul saw all of these things as a kind of righteousness by which He deserved citizenship in the Lord’s kingdom. Yet that meeting with Jesus changed everything (Acts 9:3–22). He saw that blamelessness, while a praiseworthy goal, is not the perfection by which God declares someone righteous. He realized that he was using the Law wrongly, making conformity to it his chief goal rather than the hope of knowing the One to whom the Law points. In sum, Paul’s conversion showed him that anything he thought to be gain was actually loss, that his only hope for redemption was the righteousness that “comes through faith in Christ, the righteousness from God that depends on faith” (Phil. 3:9), not the righteousness sinners try to earn by observing the Law.
Thus, Paul realized that to be righteous in Christ was fully contrary to seeking his own righteousness based on his own works of the Law. In fact, he had to renounce his attempts to make himself right with God and instead rely only on divine grace. This lesson, in fact, was what he was supposed to learn from the law of Moses anyway. The Law was given after the Lord saved the Israelites from Egypt as a means by which they could know Him, not a vehicle by which they, as sinners, could earn their own righteousness (Ex. 10:1–2; 20:1–17). Studying the Law in this way means that people come to know God in Christ, to see that there is nothing of greater worth than knowing the Savior who reconciles us to the Father. Understanding the Law rightly means that we make gaining Christ our highest goal.