Jesus encountered two demon-possessed men during His brief stay in Gadara, though accounts vary on the number, with one man possibly being more prominent and aggressive. Jesus acknowledged the reality of the Devil and demons, recognizing their evil influence over human beings with serious intensity and authority, openly declaring the evil in people's minds and bodies as originating from Satan, the source of evil. Demonic powers are exercised in three ways: directly by the Devil himself, through demons subject to him, and via human beings he influences or possesses. Those who reject God's authority become subject to Satan's supernatural power, allowing their personality and will to be overtaken by deceiving, lawless spirits. Demon possession occurs when a spiritual parasite intrudes upon the human body and mind, causing conflict and disharmony, often following a person's willingness to entertain evil thoughts or engage in immorality, hatred, or greed. This can lead to sudden possession when a person loses self-control. There is a distinction between demon influence and possession. Most people experience some level of demonic influence through Satan's broadcast of evil attitudes, enticing them to sin with subtle suggestions that can escalate to full possession, rendering them captive to the Devil and sinking into degradation. Demons can possess both minds and bodies, sometimes being invited as familiar spirits, leading to increased sensuality, violence, and physical, mental, and spiritual disorders, often resulting in insanity. Not all mental disorders stem from demonic possession, though conditions like insanity, epilepsy, blindness, fevers, and various mental illnesses can be symptoms or aggravated by such dark powers. In the case of the Gadarene demoniac, his insanity was compounded by an extreme demonic element, a result of his own wickedness, though possession is distinct from mere madness. The Devil, as the prince of the power of the air, influences the world's current way of life, working in those who disobey, leading them to yield to his authority and become slaves to evil.

In the accounts of Matthew 8:28-34, Mark 5:1-20, and Luke 8:26-39, Jesus Christ commands unclean spirits to leave two men, demonstrating His authority over demons. These demons, though compelled to obey Jesus, resist initially, reluctant to abandon their victims. Christ, with His great power, could have forced them out immediately, but exercises wise, gentle, and cautious concern for the men's well-being. In a distinct incident recorded in Mark 9:26-27, a single demon, upon leaving a man, causes severe convulsions, leaving the man as if dead until Jesus lifts him up, restoring him. Jesus addresses the possessed men as if under the control of a single spirit, but the response, naming itself Legion, reveals a multitude of demons led by one will, united in purpose. Mark notes that about two thousand swine, into which the demons enter after the exorcism, reflect the horrific extent of the men's possession, each demon possessing its own personality yet operating as one. Regarding the demons' request to enter the swine, as seen in Matthew 8:31, Mark 5:12, and Luke 8:32, Christ does not send them into the swine Himself but permits their exit from the men, allowing the demons to act by divine consent. The swine, a symbol of uncleanness, become an appropriate vessel for these unclean spirits, unlike the serpent, another animal linked to demonic presence, which symbolizes deception and shrewdness. The exorcism brings profound changes to the men, as described in Mark 5:15 and Luke 8:35. Initially restless and wandering, they find rest and a new posture of sitting calmly after deliverance. Their attitude shifts dramatically; once avoiding Christ, they now revere Him and desire to follow Him, though Jesus directs them to witness to others instead. Their appearance transforms as well; previously unclothed, they are now dressed, reflecting spiritual cleanness through modesty and improved demeanor. Their sanity returns, replacing the chaos of possession with order, though they must guard against repossession by filling their minds with God's truth. Finally, they gain self-control, their thoughts and actions now aligned under a right mind, contrasting the uncontrollable nature of the demons who once dominated them, recognizing only God's authority through Christ.

In the exploration of the spirit world, the influence of demons emerges as a significant concern when seeking knowledge beyond what God has revealed. During the period between the Testaments, some Jews, driven by curiosity, attempted to expand their understanding of angels, developing an extensive angelology. Initially, this pursuit may have been benign, but it became perilous as demons began to shape their thoughts. These malevolent entities, sometimes referred to as demiurges by figures like Philo and the Neoplatonists, contributed to the rise of Gnosticism, leading to distorted beliefs. This serves as a cautionary tale about the dangers of straying from God's Word, as such deviations invite the deceptive influence of demons and result in spiritual trouble.

Satan, recognized by Jesus Christ as the ruler of this world, does not govern alone but commands a vast army of fallen angels known as demons. These evil entities, possibly numbering in the millions, are described by the apostle Paul as principalities, powers, and rulers of the darkness of this age, engaging in spiritual warfare against humanity. God occasionally reveals in His Word how these malevolent forces are permitted to influence the rulers of nations to fulfill divine purposes, as seen when an evil spirit deceived the prophets of Ahab, leading to his downfall in battle. In the prophecies concerning the end times near the second coming of Jesus Christ, God depicts how satan and his demons will be cast down to earth, instigating great persecution against the Church of God. The dragon, symbolizing satan, will empower a future world-ruling empire and its leader with authority and might, mirroring the temptation offered to Jesus Christ. This empire will dominate all aspects of life, enforcing idolatry and controlling global economies, bringing severe trials to God's people. Additionally, demons invisibly influence human decisions, broadcasting attitudes and thoughts that lead to atrocities and wars throughout history. As long as satan and his demons hold sway over this world, they will remain the hidden force behind global events, perpetuating misery through envy, jealousy, lust, and greed. However, God's prophecies assure that Jesus Christ will ultimately depose satan, binding him to end his influence, ushering in a millennium of peace and prosperity upon Christ's return.