At various times in Christian history, attempts have been made to classify these beings according to various proposed demonic hierarchies.
According to most Christian demonology demons will be eternally punished and never reconciled with God. Other theories postulate a Universal reconciliation, in which Satan, the fallen angels, and the souls of the dead that were condemned to Hell are reconciled with God. This doctrine is today often associated with the Unification Church. Origen, Jerome and Gregory of Nyssa also mentioned this possibility.
In contemporary Christianity, demons are generally considered to be angels who fell from grace by rebelling against God. Some contest that this view, championed by Origen, Augustine and John Chrysostom, arose during the 6th century. Another theory that may have preceded or co-existed with the hypothesis of fallen angels was that demons were ostracized from Heaven for the primary sin of mating with mortal women, giving rise to a race of half-human giants known as the Nephilim. That theory is accepted by some contemporary Christian sects.
There are still others who say that the sin of the angels was pride and disobedience. It seems quite certain that these were the sins that caused Satan's downfall (Ezek. 28). If this be the true view then we are to understand the words, "estate" or "principality" in Deuteronomy 32:8 and Jude 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.") as indicating that instead of being satisfied with the dignity once for all assigned to them under the Son of God, they aspired higher.
According to the Bible, the fall of the Adversary is portrayed in Isaiah 14:12-14 and Ezekiel 28:12-19. However, the connection between Isaiah 14:12-14 and the fall is mostly based on mistranslation and tradition. The King James Version (KJV), popularamong most Christian sects, reads:"How art thou fallen from heaven, O Lucifer, son of the morning! [how] art thou cut down to the ground, which didst weaken the nations! For thou hast said in thine heart, I will ascend into heaven, I will exalt my throne above the stars of God: I will sit also upon the mount of the congregation, in the sides of the north: I will ascend above the heights of the clouds; I will be like the most High" (Isaiah 14:12:-14). The word "Lucifer" was inspired by the Latin Vulgate, a translation that the authors of the KJV adhered to in several occasions to elucidate Christian traditions (see KJV, "The Project"). Lucifer is a Latin word meaning "light-bearer" (from lux, lucis, "light", and ferre, "to bear, bring"), a Roman astrological term for the "Morning Star", the planet Venus. The word Lucifer was the direct translation of the Septuagint Greek heosphoros, ("dawn-bearer"); (cf. Greek phosphoros, "light-bearer") and the Hebrew Helel, ("Bright one"). The word does not specifically refer to Satan. To the contrary, in context, Isaiah 14:12-14 actually refers to one of the popular honorific titles of a Babylonian king (see Isaiah 14:4 for context); however, later interpretations of the text, and the influence of embellishments in works such as Dante's The Divine Comedy and Milton's Paradise Lost, led to the common idea in Christian mythology and folklore that Lucifer was a poetic appellation of Satan (see Lucifer for more information).
Ezekiel 28:12-19, in context, refers to the King of Tyrus (see Ezekiel 28:2 for context). The passage, however, is popularly attributed as a reference to, or allegory of, Satan, and even by some commentators, an allegory of the fall of Adam.
The Christian teachings of [source missing] built upon later Jewish traditions that the Adversaryand the Adversary's host declared war with God, but that God's army, commanded by the archangel Michael, defeated the rebels. Their defeat was never in question, since God is by nature omnipotent, but Michael was given the honour of victory in the natural order; thus the rise of Christian veneration of the archangel Michael, beginning at Monte Gargano in 493, reflects the full incorporation of demons into Christianity.
According to tradition, God then cast God's enemies from Heaven to the abyss, into a newly created prison called Hell, where all God's enemies should be sentenced to an eternal existence of pain and misery. This pain is not all physical; for their crimes, these angels, now called demons, would be deprived of the sight of God, this being the worst possible punishment.
An indefinite time later (some biblical scholars believe that the angels fell sometime after the creation of living things), when God created the earth and life, the Adversary and the other demons were allowed to tempt humans or induce them to sin by other means. The first time the Adversary did this was as a serpent in the earthly paradise called the "Garden of Eden" to tempt Eve, who became deceived by Satan's evil trickery. Eve then gave Adam some of the forbidden fruit and both of their eyes were opened to the knowledge of good and evil.