job 2:4 And Satan answered the LORD, and said, Skin for skin, yea, all that a man hath will he give for his life. - Free Bible Online

      4. Skin for skin--a proverb. Supply, "He will give." The "skin" is figurative for any outward good. Nothing outward is so dear that a man will not exchange it for some other outward good; "but" (not "yea") "life," the inward good, cannot be replaced; a man will sacrifice everything else for its sake. Satan sneers bitterly at man's egotism and says that Job bears the loss of property and children because these are mere outward and exchangeable goods, but he will give up all things, even his religion, in order to save his life, if you touch his bones and flesh. "Skin" and "life" are in antithesis [UMBREIT]. The martyrs prove Satan's sneer false. ROSENMULLER explains it not so well. A man willingly gives up another's skin (life) for his own skin (life). So Job might bear the loss of his children, &c., with equanimity, so long as he remained unhurt himself; but when touched in his own person, he would renounce God. Thus the first "skin" means the other's skin, that is, body; the second "skin," one's own, as in Ex 21:28.

JFB.