It is biblical to believe in demons and that what people believe to be hauntings are either the mere illusions of charlatans or involve actual demonic activity, the visiting by human spirits. It is biblical to not become obsessed with them and with the spirit world. Nowhere in Scripture can you find any precedence for doing so.
There are numerous instances in which evil angels (demons) are recorded as interacting with people. They are able to manipulate physical things as well. In Job 1:12-19, they manipulate people to do evil; they cause fire from the sky to consume herds of sheep; they cause a wind to blow down the house in which Job's children were staying. In the gospels a number of instances are recorded of demons possessing people (Mt. 8:16,28f.; 9:32-33; 12:24; Mt. 15:22; Mt. 17:18; etc.) In these incidents, and several others, the manifestation of the demon possession involved some physical ailment (muteness, epilepsy, blindness, but sometimes supernatural strength). They also possessed the pigs before they ran into the waters and drown in Mt. 8:28f.
The belief in Satan and his army of demons first appears in Jewish writings after 300 BCE. At the time of the 1st century CE, it is a well developed concept in Palestine. There are literally dozens of passages referring to demon possession causing mental and physical illnesses. A major feature of Jesus' ministry is portrayed as curing people of demonic possession through exorcism.
Matthew 4:24: "...they brought unto him [Jesus] all sick people that were taken with divers diseases and torments, and those which were possessed with devils, and those which were lunatick, and those that had the palsy..."
Matthew 8:16: "When the even was come, they brought unto him many that were possessed with devils..."
Matthew 8:28-34: "And when he [Jesus] was come to the other side into the country of the Gergesenes, there met him two possessed with devils, coming out of the tombs, exceeding fierce..." (KJV; devils are normally translated as demons in other Bible versions). Matthew 9:32-33: "As they went out, behold, they brought to him a dumb man possessed with a devil."
Matthew 10:1: "And when he had called unto him his twelve disciples, he gave them power against unclean spirits, to cast them out, and to heal all manner of sickness and all manner of disease."
Matthew 12:22: "Then was brought unto him one possessed with a devil, blind, and dumb..."
Matt 12:43-45: "When the unclean spirit is gone out of a man, he walketh through dry places, seeking rest, and findeth none."
Matthew 15:22: "And, behold, a woman of Canaan came out of the same coasts, and cried unto him, saying, Have mercy on me, O Lord, thou Son of David; my daughter is grievously vexed with a devil."
Matthew 17:14-18: "There came to him a certain man, kneeling down to him, and saying, Lord, have mercy on my son: for he is lunatick, and sore vexed...And Jesus rebuked the devil; "
Mark 1:23: "And there was in their synagogue a man with an unclean spirit; and he cried out..."
Mark 3:11: "And unclean spirits, when they saw him, fell down before him, and cried..."
Mark 3:22-26: "And the scribes which came down from Jerusalem said, He hath Beelzebub, and by the prince of the devils casteth he out devils."
Mark 5:2-20: "...there met him [Jesus] out of the tombs a man with an unclean spirit, Who had his dwelling among the tombs; and no man could bind him, no, not with chains: Because that he had been often bound with fetters and chains, and the chains had been plucked asunder by him, and the fetters broken in pieces: neither could any man tame him. And always, night and day, he was in the mountains, and in the tombs, crying, and cutting himself with stones."
Mark 6:7: "And he called unto him the twelve, and began to send them forth by two and two; and gave them power over unclean spirits;"
Mark 7:2: "For a certain woman, whose young daughter had an unclean spirit, heard of him, and came and fell at his feet:"
Mark 9:17-25: "I have brought unto thee my son, which hath a dumb spirit; And wheresoever he taketh him, he teareth him: and he foameth, and gnasheth with his teeth, and pineth away:... and when he saw him, straightway the spirit tare him; and he fell on the ground, and wallowed foaming...[Jesus] rebuked the foul spirit..."
Mark 9:38: "...Master, we saw one casting out devils in thy name, and he followeth not us..."
Mark 16:9: "...Jesus...appeared first to Mary Magdalene, out of whom he had cast seven devils."
Mark 16:17: "And these signs shall follow them that believe; In my name shall they cast out devils..."
Luke 4:33: "And in the synagogue there was a man, which had a spirit of an unclean devil, and cried out with a loud voice..."
Luke 4:41: "and devils also came out of many, crying out..."
Luke 8:2-3 "And certain women, which had been healed of evil spirits and infirmities, Mary called Magdalene, out of whom went seven devils, And Joanna the wife of Chuza Herod's steward, and Susanna, and many others..."
Luke 8:33: "Then went the devils out of the man, and entered into the swine: and the herd ran violently down a steep place into the lake, and were choked."
Luke 9:38-42: "...a man of the company cried out, saying, Master, I beseech thee, look upon my son: for he is mine only child. And, lo, a spirit taketh him, and he suddenly crieth out; and it teareth him that he foameth again, and bruising him hardly departeth from him....And Jesus rebuked the unclean spirit..."
Luke 10:17: "And the seventy returned again with joy, saying, Lord, even the devils are subject unto us through thy name."
Luke 11:14: "And he [Jesus] was casting out a devil, and it was dumb..."
Luke 11:15: "But some of them said, He casteth out devils through Beelzebub the chief of the devils."
John 7:20-21: "The people answered and said, Thou hast a devil: who goeth about to kill thee?"
John 8:48-49: "Then answered the Jews, and said unto him, Say we not well that thou art a Samaritan, and hast a devil?"
John 10:20: "And many of them said, He hath a devil, and is mad; why hear ye him?"
A number of references relate to the final destiny of Satan and his demons. They are to be thrust into Hell, described as a lake of fire. In these passages, Satan's angels apparently refer to his demons:
Matthew 25:4: "Then shall he say also unto them on the left hand, Depart from me, ye cursed, into everlasting fire, prepared for the devil and his angels."
1 Peter 2:4: "For if God spared not the angels that sinned, but cast them down to hell, and delivered them into chains of darkness, to be reserved unto judgment."
Jude 1:6: "And the angels which kept not their first estate, but left their own habitation, he hath reserved in everlasting chains under darkness unto the judgment of the great day."
Revelation 12:9: "And the great dragon was cast out, that old serpent, called the Devil, and Satan, which deceiveth the whole world: he was cast out into the earth, and his angels were cast out with him."
Demons are also mentioned elsewhere in the Christian Scriptures:
Acts 19:13-16: "And the man in whom the evil spirit was leaped on them, and overcame them, and prevailed against them, so that they fled out of that house naked and wounded."
James 2:19: "Thou believest that there is one God; thou doest well: the devils also believe, and tremble."
Revelation 9:20: "And the rest of the men which were not killed by these plagues yet repented not of the works of their hands, that they should not worship devils, and idols of gold, and silver, and brass, and stone, and of wood: which neither can see, nor hear, nor walk"
Various passages describe how Satan can adopt a spirit form, reside inside a person, and influence their thoughts and behavior in the same way as a demon can: Ephesians 2:2 describes him as a spirit who works within "the children of disobedience."
John 13:2 describes how Satan "put into" Judas Isariot's mind the decision to betray Jesus.
Acts 5:3 describes how Satan filled Ananias' heart with the decision to lie to the Holy Ghost about the proceeds of a real estate sale.
