The Facts on Angels (Harvest House, 1995) p. 18
Exactly who are the evil angels, what are some false ideas concerning them, and what are their powers?
Demons are not the spirits of dead men or a pre-Adamite race, as some people argue, for the spirits of the human dead are not free to roam (Luke 16:19-31; 2 Peter 2:9). Nor are they merely personifications of evil or of natural forces (such as the “gods” of nature), as skeptics assume. Nor are demons the superstitious designation for particular natural diseases such as epilepsy or mental illness. Scripture clearly distinguishes these disorders from demon possession, although it is possible that both can be present or that demon possession could induce mental illness.*
If we were to catalog the powers and abilities of angels given in Scripture, we would gain a glimpse into their capabilities, and hence also discern the abilities of demons as corrupted angels. However, it must never be forgotten that demons are creatures who are ultimately constrained by the sovereign power and purpose of God. When needed, the Christian has power over them (1 John 4:4; James 4:7) because Christ Himself was victorious over Satan at the cross (Hebrews 2:14; Colossians 2:15; John 12:31). Jesus proved His complete power over demons (Matthew 12:28; Mark 1:34), often casting demons out of people (Matthew 8:31; 15:22-28), and He commanded His disciples to do the same (Mark 6:13; Matthew 10:1; Luke 10:17).
*For full documentation, please see The Facts on Angels.