2 Timothy 3:8

And even Jannes and Jambres withstood Moses, so do these also withstand the truth; men corrupted in mind, reprobate concerning the faith.

Jannes and Jambres ... These were the evil magicians who withstood Moses during his appearances before Pharaoh; and Paul's identification of them here is the very earliest mention of these names which has descended to us through history. That these names have appeared in later Jewish writings in slightly different form is not a reflection against Paul, but against those writings. Though their names are not in the Old Testament, the works of these impostors are recorded in Exodus 7:11; 9:11. They could indeed counterfeit some of the miracles of Moses; but in others their weak pretensions were exposed, and their folly became evident to all. For example, when Moses cast down his rod and it became a serpent, the magicians also produced serpents; but all of their serpents were swallowed up by the serpent that came from the rod of Moses. At any time in history when the grace of God is very active, Satan always responds with his own brand of wonders. When the Holy Spirit in the Person of Christ dwelt on earth, Satan entered the arena with demon possession; the "lying miracles" of the apostate church are another example.

Reprobate concerning the faith ... This indicates that the evil men Paul spoke of had once been in the faith but had fallen away from it. "The faith" is understood subjectively in this place by some; but as Lenski wisely observed:

The Lord has not supplied us with a touchstone that may be applied to men's hearts; but he has supplied us with his word, thereby to test all that men offer as "the faith" or doctrine.[17]