Gregory the Dialogist

Who changeth the lip of the truthful, and taketh away the instruction of the aged. When the priest does not do the good that he tells, even the very word of his lips is withdrawn from him, that he may not dare to speak what he does not practise; as where it is said by the Prophet, But unto the wicked God saith, 'What hast thou to do, to declare My statutes, or that thou takest My covenant in thy mouth? Whence also he beseeches, saying, And take not the word of truth utterly out of my mouth. …

Morals on the Book of Job, Book XI ↗

Thomas Aquinas

Philosophers excel in the consideration of the truth. He says regarding these, "He alters the truth from their lips," i.e. the lips of those who are eager to speak the truth. For God sometimes darkens the mind of those men by taking away his grace so that they cannot find the truth, and, consequently cannot speak it, as Romans says, "Saying that they were wise, they have become foolish." (1:22) Old men also excel in the direction of the young, and in their regard he continues, "he takes away instruction from the elders," either …

Commentary on Job ↗