Gregory the Dialogist

Whence it is still further added, For thine iniquity teacheth thy mouth, and thou followest the tongue of the crafty. 'Iniquity teaches the mouth,' when there is conceived by a bad life somewhat to be spoken of a worse kind. Now because blessed Job was free in speech in proportion as he was holy in action, by his friends, who hold the type of heretics, he is found fault with at once on the grounds of a wicked life and of a bold mouth, so that it should be said, Thine iniquity teacheth thy mouth. …

Morals on the Book of Job, Book XII ↗

Thomas Aquinas

Job had not disputed with God from pride, but out of confidence in the truth. But Eliphaz rashly judged this to flow from wickedness and so he then says, "For your wickedness has taught your tongue," as if to say: It is apparent from the effect that you blaspheme and so he then says, "and you imitate the tongue of blasphemers." In reality, the man who blasphemes denies the justice of God. But one who disputes with God about his justice seems to imitate the language of the blasphemers. …

Commentary on Job ↗