Malbim: Tzufar said "v'Chafarta la'Vetach Tishkav", "umi'Tzaharayim Yakum Chaled" (11:18, 17) - he will live again after death. Iyov responds, if only I would be hidden in the grave temporarily, until Your anger passes! You would set a time how long I must be there, and afterwards remove me and revive me! However, this cannot be (refer to 14:14:1:1).