3 Long ago this wealthy proprietor and still wealthier father was made by a sudden stroke destitute and bereaved. But as, in spite of all that befell him, he had not sinned before God or spoken foolishly, the Lord— exulting in the victory of his servant and regarding Job's patience as His own triumph— said to the devil: “Have you considered my servant Job, that there is none like him in the earth, a perfect and an upright man, one that fears God and eschews evil? And still he holds fast his integrity?” He finely adds the last clause because it is difficult for innocence to refrain from murmuring when it is overborne by misfortune; and to avoid making a shipwreck of faith when it sees that its sufferings are unjustly inflicted.
The devil answered the Lord and said: “Skin for skin, yea, all that a man has will he give for his life. But put forth your hand now, and touch his bone and his flesh, and he will curse you to your face.” See how crafty the adversary is, and how hardened in sin his evil days have made him! He knows the difference between things external and internal. He knows that even the philosophers of the world call the former ἀ διάφορα, that is indifferent, and that the perfection of virtue does not consist in losing or disdaining them.
It is the latter, those that are internal and objects of preference, the loss of which inevitably causes chagrin. Wherefore he boldly contradicts what God has said and declares that Job deserves no praise at all; since he has yielded up no part of himself but only what is outside himself, since he has given for his own skin the skins of his children, and since he has but laid down his purse to secure the health of his body. From this your sagacity may perceive that your trials have so far only reached the point at which you give hide for hide, skin for skin, and are ready to give all that you have for your life.
The Lord has not yet stretched forth His hand upon you, or touched your flesh, or broken your bones. Yet it is when such afflictions as these are laid upon you that it is hard not to groan and not to 'bless' God to His face, that is to curse Him. The word 'bless' is used in the same way in the books of Kings where it is said of Naboth that he 'blessed' God and the king and was therefore stoned by the people. But the Lord knew His champion and felt sure that this great hero would even in this last and severest conflict prove unconquerable.
Therefore He said: “Behold he is in your hand; but save his life.” The holy man's flesh is placed at the devil's disposal, but his vital powers are withheld. For if the devil had smitten that on which sensation and mental judgment depend, the guilt arising from a misuse of these faculties I would have lain at the door not of him who committed the sin but of him who had overthrown the balance of his mind.
Source: Letters (New Advent)