John Gill Commentary Galatians 1:14

"and I advanced in the Jews` religion beyond many of mine own age among my countrymen, being more exceedingly zealous for the traditions of my fathers." — Galatians 1:14 (ASV)

And profited in the Jews' religion
Or "in Judaism"; and the more he did so, or was versed in, and wedded to their principles, the more violent a persecutor he was. He was under a very considerable master, Gamaliel, a Rabbi of great note among the Jews; and he himself a youth of uncommon natural abilities, so that his proficiency in Jewish learning was very great; even, as he says,

above many my equals in mine own nation :
not proselytes in other nations, but such as were natives of his own country: or were "in his own kindred", his near relations, who were his contemporaries, of the same age with him; and very modestly he says "many", not "all":

being more exceedingly zealous of the traditions of my fathers :
he had a zeal, but, not according to knowledge; and a greater degree of it than the rest of his countrymen; and that not so much for the written law delivered to his fathers, as for the oral law, the traditions and customs of his ancestors; which had been handed down, as they pretended, from one to another, and were now swelled to an almost infinite bulk; and mean the traditions of the elders, condemned by Christ, as making void the commandments of God: now his close attachment to, and eager zeal for these traditions, put him upon using more violent measures in persecuting the saints, and further off from the Gospel of Christ: and now from this account of himself it is a clear point, that during this period of his life he could never have received the Gospel from men, which is his view in giving it.