Old Testament history presents occasional mention of their existence and agency; but it was during the time when Christ was upon the earth that evil spirits manifested their power in the most striking manner. Christ had come to enter upon the plan devised for man's redemption, and Satan determined to assert his right to control the world. He had succeeded in establishing idolatry in every part of the earth except the land of Palestine. To the only land that had not fully yielded to the tempter's sway, Christ came to shed upon the people the light of heaven. Here two rival powers claimed supremacy. Jesus was stretching out His arms of love, inviting all who would to find pardon and peace in Him. The hosts of darkness saw that they did not possess unlimited control, and they understood that if Christ's mission should be successful, their rule was soon to end. Satan raged like a chained lion and defiantly exhibited his power over the bodies as well as the souls of men.
The fact that men have been possessed with demons, is clearly stated in the New Testament. The persons thus afflicted were not merely suffering with disease from natural causes. Christ had perfect understanding of that with which He was dealing, and He recognized the direct presence and agency of evil spirits.
A striking example of their number, power, and malignity, and also of the power and mercy of Christ, is given in the Scripture account of the healing of the demoniacs at Gadara. Those wretched maniacs, spurning all restraint, writhing, foaming, raging, were filling the air with their cries, doing violence to themselves, and endangering all who should approach them. Their bleeding and disfigured bodies and distracted minds presented a spectacle well pleasing to the prince of darkness. One of the demons controlling the sufferers declared: "My name is Legion: for we are many." Mark 5:9. In the Roman army a legion consisted of from three to five thousand men. Satan's hosts also are marshaled in companies, and the single company to which these demons belonged numbered no less than a legion.
At the command of Jesus the evil spirits departed from their victims, leaving them calmly sitting at the Saviour's feet, subdued, intelligent, and gentle. But the demons were permitted to sweep a herd of swine into the sea; and to the dwellers of Gadara the loss of these outweighed the blessings which Christ had bestowed, and the divine Healer was entreated to depart. This was the result which Satan designed to secure. By casting the blame of their loss upon Jesus, he aroused the selfish fears of the people and prevented them from listening to His words. Satan is constantly accusing Christians as the cause of loss, misfortune, and suffering, instead of allowing the reproach to fall where it belongs-- upon himself and his agents.
But the purposes of Christ were not thwarted. He allowed the evil spirits to destroy the herd of swine as a rebuke to those Jews who were raising these unclean beasts for the sake of gain. Had not Christ restrained the demons, they would have plunged into the sea, not only the swine, but also their keepers and owners. The preservation of both the keepers and the owners was due alone to His power, mercifully exercised for their deliverance.
Furthermore, this event was permitted to take place that the disciples might witness the cruel power of Satan upon both man and beast. The Saviour desired His followers to have a knowledge of the foe whom they were to meet, that they might not be deceived and overcome by his devices. It was also His will that the people of that region should behold His power to break the bondage of Satan and release his captives. And though Jesus Himself departed, the men so marvelously delivered, remained to declare the mercy of their Benefactor.