SCRIPTURE 2 Timothy 3:8 “Now as Jannes and Jambres withstood Moses, so do these also resist the truth: men of corrupt minds, reprobate concerning the faith.” 

COMMENTARY Here the person described, as those who opposed Moses, knew of God but did not follow.  Here reprobate (Greek adokimos) means “that which does not prove itself to be such as it ought.”  Here we see that they are people who do claim to have faith but act inconsistent with what they believe, not proving themselves.  It does not say they did not have faith (as in void of faith) but rather they are reprobate concerning the faith, again meaning they do not act consistent with that faith.