3:4b For the sake of the argument Paul adopted the Judaizers' attitude of confidence in the flesh. He did this to show that his rejection of Jewish advantages was not because he lacked them.108
3:5 Circumcision of the flesh was one thing that the Judaizers trusted in for acceptance by God. Paul had been circumcised on the eighth day after his birth as the Law of Moses prescribed (Lev. 12:3; cf. Gen. 17:12). He had not received circumcision later in life as many people did who converted to Judaism (e.g., Acts 16:3).
Paul was also an Israelite by birth, not a Gentile Jewish proselyte.
Furthermore he was a member of the tribe of Benjamin. Benjamin was the younger of the two sons born to Jacob's favorite wife, Rachel. Benjamin was the only son of Jacob who was born in the Promised Land. The tribe of Benjamin provided many noble warriors throughout Israel's history (cf. Hos. 5:8). Israel's first lawful king came from Benjamin. Jerusalem and the temple stood within Benjamin's territory. This tribe alone, beside Judah, remained loyal to David's house when the monarchy divided. The feast of Purim celebrated the salvation of the Jews by a Benjamite, Mordecai. After the Exile, Benjamin and Judah formed the core of the restoration community. Of course, this tribe's history was not without its shame as well (e.g., Saul's failures, the Gibeans' atrocity that led to the civil war that almost wiped this tribe out, etc.). Nevertheless Paul could legitimately take pride in his Benjamite heritage.
A "Hebrew of Hebrews"means that Paul's parents brought him up as a strict Jew. Specifically he learned the Hebrew language and studied the Old Testament in the original tongue, not like so many other Jews of the Diaspora who could only speak and read Aramaic.
Paul had chosen to join the party of the Pharisees, the most orthodox of the sects within Judaism in his day. The Pharisees were punctilious in their observance of the Mosaic Law.109
"Not content merely to obey the Law of Moses, the Pharisees bound themselves also to observe every one of the myriad of commandments contained in the oral Law, the interpretive traditions of the Scribes. The most ardent of the Pharisees scrupulously avoided even accidental violations of the Law and did more than they were commanded to do . . . . Paul, a son of Pharisees (Acts 23:6), and a disciple of the great Pharisee, Gamaliel (Acts 5:34; 22:3), chose to be a Pharisee himself and set himself to be the most earnest of the earnest observers of the Jewish Law (Gal 1:14). Pharisee' for Paul was not a term of reproach, but a title of honor, a claim to the highest degree of faithfulness and sincerity in the fulfilment [sic] of duty to God as prescribed by the divine Torah' (Beare)."110
3:6 He had been a zealous promoter of Judaism even to the point of persecuting Christians to death. He had been an outstanding Pharisee.
Paul's obedience to the Law of Moses as it regulated external behavior had been without blame (Gr. amemptos, cf. 2:15). Clearly Paul was not claiming that he had done all that God required in the Law. Had this been true of him he would not have put Christians to death. However, he was very conscientious about what the Law required.
"Like most religious' people today, Paul had enough morality to keep him out of trouble, but not enough righteousness to get him into heaven! It was not bad things that kept Paul away from Jesus--it was good things! He had to lose his religion' to find salvation."111
