Gregory the Dialogist

Thou hast set firm thine heart, and stretched out thine hands towards Him. The heart is not here said to be 'set firm' by virtue but by insensibility, for every soul that submits itself to the consideration of the interior severity, is directly softened by the fear thereof; and the shaft of divine dread enters into him, in that he carries weak bowels through humility. But he that is hardened by obstinacy in insensibility, as it were sets his heart firm, that the darts of heavenly fear may not pierce it. …

Morals on the Book of Job, Book X ↗

Thomas Aquinas

He seemed to say this as an insult to Blessed Job because he takes Job's words as an argument with God as with an equal when he said, "May he withdraw his rod from me, let terror of him not frighten me. I will speak and not be afraid of him." (9:34) So he continues, "But you have hardened your heart," so you defend your evil. Yet, "You have stretched out your hands to God," in this condition of hardness of heart in prayer when you said, "I will say to God: Do not condemn me." (9:34) So your prayer is useless.

Commentary on Job ↗