Gregory the Dialogist

Neither is my strength the strength of stones, nor is my flesh of brass? For what have we here denoted by 'brass' and 'stones' save the hearts of the insensate, who oftentimes even receive the strokes of the Most High, and yet they are not softened by any strokes of discipline? Contrary whereunto, it is said to the Elect through the Prophet, by promise from the Lord, I will take the stony heart out of you, and will give you a heart of flesh. …

Morals on the Book of Job, Book VII ↗

Thomas Aquinas

To explain this he says, "My strength is not the strength of a stone." For a stone experiences strength without experiencing feeling, but a man experiences strength along with the emotional experience of harmful things. So he continues, "nor is my flesh bronze", i.e. without feeling because however strong the reason of a mortal man may be, he still must experience the feeling of pain on the part of the flesh. By this he refutes the attempted rebuke of Eliphaz who censured the very existence of sadness in Blessed Job. …

Commentary on Job ↗

Bonaventure

The third middle way is fortitude, which is concerned with fears and acts of valor. A man needs it in order to be neither fainthearted nor rash, but that he be able to bear frightful trials and even death. For some men do fall into cowardice and faintheartedness. Hence, in Job: "Have I the strength of stones, or is my flesh of bronze?" And so, fortitude is in the soul, not in the flesh. Better is the patient spirit than the lofty spirit. …

Collations on the Hexaemeron, Collation 5 ↗