13 For you have heard of my former conduct in Judaism, how I persecuted the church of God beyond measure and tried to destroy it.
14 And I advanced in Judaism beyond many of my contemporaries in my own nation, being more exceedingly zealous for the traditions of my fathers.
Paul's personal history (v.13) proves that his gospel was not from men but from God. He was saying, "How could I have received my gospel from men, or from the 12 apostles? You yourselves know how earnestly I sought to destroy their church."
Paul had been on his way to Damascus to wipe out the apostles' church. How could they have appointed him an apostle?
There was at that time only one nation which God recognized as His own. And that nation, Israel, rebelled against Him. Who inspired and led that rebellion? Saul of Tarsus. And who was Saul of Tarsus? A wicked ruffian? No! He was one of the chosen race, and was highly respected by his nation. He was a scrupulous observer of the law, zealous of the traditions of his fathers. Was he so ignorant of the Old Testament prophecy that he did not recognize Christ? No, he was a Pharisee, the son of a line of Pharisees, a Hebrew of the Hebrews, of the tribe of Benjamin, a spiritual leader in Israel with a profound knowledge of the law and the prophets. Yet this man led his nation in bitter persecution against the followers of Jesus, determined to stamp out the very name and memory of Jesus Christ of Nazareth. — Studies in Galatians, by Cornelius R. Stam, page 77.
you have heard (v.13) — Paul often mentioned his personal history when he preached (Acts 22 and 26) and surely did so to the Galatians.
former (v.13) — before he was saved.
conduct (v.13) = conduct in regard to others, manner of life
Judaism — not the beliefs, but the practices as the scribes and Pharisees had developed them by tradition beyond what was instituted by God. Paul's Judaism was apostate. He knew no personal relationship with God. It was all outward expression with no inward faith. He later, after his salvation, gained a proper understanding of the Old Testament.
persecuted = pursue earnestly (Acts 9:13-14).
church of God (v.13) = called-out assembly. Jewish believers in Jerusalem, not the body of Christ here.
destroy it (v.13) — ruin, to the death (Acts 22:4)
advanced (v.14) = to strike forward, advance, blaze a way through. Paul pioneered in his studies, cutting new paths.
my contemporaries (v.14) — students his own age in the rabbinical schools
more exceedingly (v.14) — by comparison (Philippians 3:4-6)
zealous (v.14) — uncompromising, unquestioned loyalty
traditions (v.14) — interpretations of Moses' law (Mark 7:3-13)
fathers (v.14) — Pharisees. Not, in this case, Moses, etc. Paul's father was a Pharisee. It was the tradition of his own family.
Paul was profiting as a persecutor. Why would he change his message if he hadn't heard it from God? And it wasn't just a matter of profit, he was zealous. He believed in the rightness of his actions. There was nothing on earth that could have changed his mind.
He is speaking here of the hereditary traditions of his family. He was the son of a Pharisee. These Pharisaic traditions had been ingrafted on the law and had made that law void (Matthew 15:1-6). Thus, he could not have had a true conception of the Mosaic economy, and when he was converted, he found it necessary to restudy his Old Testament scriptures in the light of the revelations given him in Arabia, and under the instruction of the Holy Spirit. If Paul had intended to refer to the Mosaic law, either by itself or in connection with the Pharisaic traditions, he would have mentioned the law by itself or along with the traditions. He is here speaking of the way in which his brilliant advancement in Judaism had displayed itself. In short, the great apostle before his conversion, was occupied more with human legal enactments and practices as ingrafted upon the Word of God, and as interpreting that Word, than he was with the Word of God itself. The traditions of his fathers included the religious definitions handed down in respect to doctrine, ritual, asceticism, interpretation of Scripture, and conduct of life. Thus, Paul shows that he was not at the time of his conversion and appointment to the office of apostle, under such influences of in such a frame of mind as to make the reception of the gospel by him from human instruction possible. Only a supernatural revelation could have effected it. Therefore, proof is established that neither Paul's office as apostle nor his message came by way of a human channel, but direct from God. — Galatians in the Greek New Testament, by Kenneth S. Wuest, page 48-49