G1226–διαβεβαιόω–diabebaioō

willing to be teachers of law, not understanding either the things they say, nor concerning what they asseverate,

διαβεβαιοῦνται. diabebaiountai “they confidently assert.”

Stedfast `is' the word; and concerning these things I counsel thee to affirm fully, that they may be thoughtful, to be leading in good works -- who have believed God; these are the good and profitable things to men,

διαβεβαιοῦσθαι diabebaiousthai “to affirm strongly”