The miracles worked by Christ were arguments for the faith which He taught. Now, by the power of His Godhead He was to rescue those who would believe in Him, from the power of the demons; according to John 12:31: "Now shall the prince of this world be cast out." Consequently it was fitting that, among other miracles, He should also deliver those who were obsessed by demons.
Thomas Aquinas, Summa Theologiae 3.44.1.
