Adam Clarke on Job 2:4

Skin for skin - That is, A man will part with all he has in the world to save his life; and he will part with all by piecemeal, till he has nothing left on earth, and even be thankful, provided his life be spared. Thou hast only destroyed his property; thou hast left him his life and his health. Thou hast not touched his flesh nor his bone; therefore he is patient and resigned. Man, through the love of life, will go much farther: he will give up one member to save the rest; yea, limb after limb as long as there is hope that, by such sacrifices, life may be spared or prolonged. This is the meaning given to the passage by the Targum; and, I believe, the true one; hence, Job 2:6, the Lord says, Save his life.