Commentaire sur Job 2:4

Skin for skin One limb for another limb. It is human nature that, when one sees a sword coming toward his head, he protects it with his arm in front of it. Surely a person will give all the money he has.

Satan, however, is unrepentant and unconvinced. He demands a further test, this time one whose torment Job himself must bear. He argues that all that has been shown so far is that Job was not particularly sensitive to the loss of his possessions and children.
'A skin for a skin!' cries Satan. Job's own body has not been touched and it is only for fear that it might be that he has not yet complained against God. For it is well known that a man will always give up an outer 'skin' to save another more precious to him.

for his life For his life to protect it. Because this person knows that he is liable to lose his life, he does not worry about his money.

Man is a negotiator by nature and so will give everything he has to save his life. No matter how much is taken away from him, so long as he still lives, man always has something left that he will try to protect and for which he will bargain.