Pope Leo: God Uses Satan's Works to Thwart Him

In Sermon 62, Pope Leo the Great says of Satan:

[H]e inflicted a punishment on the Son of God, which was turned to the healing of all the sons of men. He shed righteous Blood, which became the ransom and the drink for the world's atonement. The Lord undertook that which He chose according to the purpose of His own will. He permitted madmen to lay their wicked hands upon Him: hands which, in ministering to their own doom, were of service to the Redeemer's work. And yet so great was His loving compassion for even His murderers, that He prayed to the Father on the cross, and begged not for His own vengeance but for their forgiveness, saying, "Father, forgive them, for they know not what they do (Luke 23:34) ."