G1226–διαβεβαιόω–diabebaioō

desiring to be teachers of the law, though they understand neither what they say, nor about what they strongly affirm.

διαβεβαιοῦνται. diabebaiountai “they confidently assert.”

This saying is faithful, and concerning these things I desire that you affirm confidently, so that those who have believed God may be careful to maintain good works. These things are good and profitable to men;

διαβεβαιοῦσθαι diabebaiousthai “to affirm strongly”