Since demons are fallen angels, they possess the same level of power and influence as angels. However, Scripture seems to indicate that God has limited their abilities (2 Thessalonians 2:6–7). The Bible indicates that not all afflictions are due to demonic influence (Matthew 10:1; Luke 8:2). The vast majority of demonic influence is spiritual, not physical.
Just then there was a man in their synagogue with an unclean spirit; and he cried out, saying, “What business do we have with each other, Jesus of Nazareth? Have You come to destroy us? I know who You are—the Holy One of God!” And Jesus rebuked him, saying, “Be quiet, and come out of him!” Throwing him into convulsions, the unclean spirit cried out with a loud voice and came out of him. | Mark 1:23–26
Jesus the Messiah understood exorcism as part of his ministry: Demons are referred to by several alternate names, including “unclean spirits” and “evil spirits.” Some of the false gods that received human sacrifices are described as actual demons (2 Chronicles 11:15; Deuteronomy 32:17).
Jesus drove out demons from individuals whom he encountered: An unclean spirit or demon is “unclean” in that it is wicked. Evil spirits are not only wicked themselves, but they delight in wickedness and promote wickedness in humans. They are spiritually polluted and impure, and they seek to contaminate all of God’s creation with their filth.
Their foul, putrid nature is in direct contrast to the purity and incorruption of the Holy Spirit’s nature. When a person is defiled by an unclean spirit, he takes pleasure in corrupt thoughts and actions; when a person is filled with the Holy Spirit, his thoughts and actions are heavenly.
When exactly God created angels is open for debate, but what is known for sure is that God created everything good because God, in His holiness, cannot create something sinful. So when Satan, who was once the angel Lucifer, rebelled against God and fell from heaven (Isaiah 14; Ezekiel 28), one third of the angelic host joined his insurrection (Revelation 12:3-4,9). There is no doubt these fallen angels are now known as the demons.