Demons are disembodies spirit beings that have an intense craving to occupy physical bodies. Apparently their first choice is a human body, but rather than remain in a disembodies condition they are willing to enter even the body of an animal - see Luke 8:32-33.
Though demons have no bodies, they have all the normally accepted marks of personality.
4. Self-awareness and
5. Ability to speak
THEIR ORIGIN: TWO MAIN THEORIES
1. They are some of the fallen angles associated with Satan in his rebellion against God.
2. They are disembodies spirits of a pre-adamic race that perished under some judgment of God not in detail in scripture.
Ephesians 6:12 & 2 Corinthians 12:2-4
It seems clear to me that even fallen angels still maintain their dwelling place somewhere in "the heavenly places. Demons appear to be earthbound creatures. They display a wide range of character traits. Some are vicious violet, supernaturally strong. Other are weak, covering, even ridiculous - characteristics one would not expect to find in angels, even when they are fallen.
It is true that for the specific purpose of tempting Adam and Eve into rebellion, Satan did temporarily come to them in the form of a serpent. But subsequent passages of scripture make it clear that he did not continue to occupy the body of a serpent. See Luke 22:3,4; Luke 13:11-16.
DEMONS IN SCRIPTURE
Demons manifest themselves through humanity under many different names. The following is a list of specific names actually applied to demons in scriptures.
IN OLD TESTAMENT
Jealousy and feeling of Jealousy - Num 5:14,30
Ill, will, evil - Judges 9:23
Distressing evil - 1 Samuel 16:14-23; 18:10; 19:9
Lying, deceiving - 1 Kings 22:22; 2 Chro 18:20-22
Just to mention some.
IN THE NEW TESTAMENT
1. Mute/Robbed of speech - Mark 9:17
2. Deaf & dumb, deaf - Mark 9:25
3. Infirmity/causing sickness - Luke 13:11
4. Divination - Acts 16:16
5. Fear Timidity - 2 Timothy 1:7
The lists given above are by no means exhaustive, but indicate the diversity of demonic activity Satan apparently has at his disposal vast numbers of demons with which to assail and torment humanity.
FLESH OR DEMONS
From the beginning, ever since man turned from God in rebellion, he has been subjected to two main spiritual evils. "Sin & Demons."
The effect of sin is universal and total Rom 3:23; Rom 6:6; Gal 5:24. The old man describes the rebellions nature of us has inherited from our first parent, Adam. Adam did not beget any children until he was in a state of rebellion against God Therefore; in every descendant of Adam there is the nature of a rebel.
Although the problem of sin is universal, the problem with demons is not. Many members of our fallen human race have come under the power of demons, but not all. There is a close connection, however, between sin and demons. If mankind had never sinned, we would never have been vulnerable to demons.
Demons continually seek to invade a person, but when the person is healthy spiritually, the spiritual, "Immune system" within the person identifies and attacks the demons, and they are not able to move in and take control.
THE REMEDY FOR EACH
In the spiritual realm, as in the physical, correct diagnosis is essential. So it is important to know, in confronting our own problems or those of other people, what we are dealing with. Is it the flesh? Or is it demons?
The question is of vital importance because the remedies are quite different:
A. The remedy for the flesh is crucifixion. By Jesus sacrificial death on the cross. Roman 6:6. But each of us must make a personal application of the cross to our fleshly nature, Paul says, therefore, in Gal 5:24 those who are Christs have crucified the flesh with its passions and desire Gal. 2:20.
B. The remedy for demons, on the other hand, as often demon stated in ministry of Jesus. Is to cast them out. These two remedies are not interchangeable. It is not possible to cast out the flesh, and it is not possible to crucify a demons.