Demons are those angels who rebelled against God along with Lucifer who is also known as Satan (meaning “adversary), the old serpent, tempter, the wicked one, ruler of this world, god of this age, murderer and father of lies (Isa. 14:12-15; Eze. 28:12-19; Jn. 12:31; 2Cor. 4:4; Matt. 4:3; 1Jn. 5:19; Jn. 8:44). Therefore, these demons are also referred to as “angels that kept not their first estate” (Jude 6); they are the fallen angels. They oppose God’s work (1Thess. 2:18), deceive the nations (Rev. 20:7-8), are proud (1Tim. 3:6), influencers of godlessness (Eph. 2:2), cruel (1Pet. 5:8), malignant (Job 2:4), and oppressors of mankind with various maladies and sicknesses (Acts 10:38; Mark 9:25). They possess the bodies of unbelievers (Matt. 8:16), can enter into a person (Lk. 22:3), can influence a person’s thinking (Acts 5:3), and can even possess the bodies of animals (Lk. 8:33).
A believer can never be demon-possessed since his body is a temple of the Holy Spirit and has no room for demons (1Cor.6:19; 1Cor.10:21).
The demons believe and tremble before God (James 2:19). Satan and his demonic angels await the judgment of God (Matt. 8:29; Rev. 20:10). The believers in Jesus Christ are called to submit to God and resist the devil (James 4:7). One sign of believers is that they shall cast out demons (Mk. 16:17).