And the LORD said to Satan, “Behold, he is in your hand; only spare his life.”
Satan, that sworn enemy to God and all good men, is here pushing forward his malicious prosecution of Job, whom he hated because God loved him, and did all he could to separate between him and his God, to sow discord and make mischief between them, urging God to afflict him and then urging him to blaspheme God.
Commenting on Job 2:1-6
So went Satan forth from the presence of the Lord,.... With leave and license, with power and authority, as the Targum; having got his commission enlarged, on a fresh grant, to do more mischief to Job, he departed directly and immediately, being eager to put in execution what he had a permission to do; See Gill on Job 1:12, and smote Job with sore boils...
but save--rather, "only spare his life." Satan shows his ingenuity in inflicting pain, and also his knowledge of what man's body can bear without vital injury.