Theophylact of Ohrid

"I lived as a Pharisee according to the strictest teaching of our religion." It is remarkable that the Pharisees too were heretics, although they studied and understood the Scriptures better than all other Jewish sects. They understood better, but not truly, because they did not possess a true understanding of the Scriptures. Thus, diligence can investigate and discuss a matter with subtlety, yet it cannot fully comprehend its essence; on the contrary, it happens that a person is deceived by his own mind.

Commentary on Acts ↗

Bede

For according to the most accurate sect of our religion, I lived as a Pharisee. For "sect," in Greek it has "heresy." Whence it is proved that at that time even a good sect was called by this term among the Greeks, which now among us is accustomed to have only a bad sense.

Retractions on Acts ↗