… All things visible and invisible…
In addition to the visible, physical creation there is an invisible world created by God. The Bible sometimes calls it “the heavens” and other times refers to it as “above the heavens.” Whatever its symbolical description in the Holy Scriptures, the invisible world is definitely not part of the physical, material universe. It does not exist in space; it has no physical dimensions. And so it cannot be located, and it has no “place” which can be “reached” by travel within the galaxies of the spatial, locatable “places” of the physically created universe.
However, the fact that the invisible, created world is purely spiritual and is not discoverable on a map of the created material spaces makes it no less real or truly existing. The invisible creation exists as different from the created material universe and, of course, as totally different from the uncreated, absolutely super-divine existence of the uncreated God.
Invisible created reality consists of the hosts of bodiless powers, generally—and somewhat incorrectly—called the angels.
Angels
Angels (which means literally “messengers”) are, strictly speaking, but one rank of the incorporeal or bodiless powers of the invisible world.
According to Orthodox Scripture and Tradition there are nine ranks of bodiless powers or the Hosts (Sabaoth means literally “armies” or “choirs” or “ranks”). There are angels, archangels, principalities, powers, virtues, dominions, thrones, cherubim, and seraphim. The latter are described as offering continual adoration and glory to God with the incessant and ever-resounding cry of Holy! Holy! Holy! (Isa 6:3; Rev 4:8). Those in the middle of the above listing are little-known to men while the angels and archangels are seen as the active workers, warriors, and messengers of Yahweh relative to this world. Thus, angels and archangels are seen to struggle against spiritual evil and to mediate between God and the world. They appear in various forms to men in both the Old and New Testaments as well as in the life of the Church. The angels are those who bring the power and presence of 
God and who are messengers of His word for the salvation of the world. The best-known of the angels are Gabriel (which means literally “man of God”), the bearer of the good news of Christ’s birth (Dan 8:16; 9:21; Lk 1:19, 26), and Michael (which means literally “who is like God”), the chief warrior of the spiritual armies of God (Dan 11:13; 12:1; Jude 9; Rev 12:7).
Generally speaking the appearances of the bodiless powers to men are described in a physical way (“six-winged, many-eyed”; or in the “form of a man”). However, it must be clearly understood that these are merely symbolical descriptions. By nature and definition the angels have no bodies and no material properties of any sort. They are strictly spiritual beings.
Evil Spirits
In addition to the created spiritual powers who do the will of God, there are, according to the Orthodox faith, those who rebel against Him and do evil. These are the demons or devils (which means literally those who “pull apart” and destroy) who are also known both in the Old and New Testaments as well as in the lives of the saints of the Church.
Satan (which means literally the enemy or the adversary) is one proper name for the devil, the leader of the evil spirits. He is identified in the serpent symbol of Gen 3 and as the tempter of both Job and Jesus (Job 1:6; Mk 1:33). He is labelled by Christ as a deceiver and liar, the “father of lies” (Jn 8:44) and the “prince of this world” (Jn 12:31; 14:30; 16:11). He has “fallen from heaven” together with his evil angels to do battle with God and his servants (Lk 10:18; Isa 14:12). It is this same Satan who “entered Judas” to effect the betrayal and destruction of Christ (Lk 22:3).
The apostles of Christ and the saints of the Church knew from direct experience Satan’s powers against man for Man’s own destruction. They knew as well Satan’s lack of power and his own ultimate destruction when man is with God, filled with the Holy Spirit of Christ. According to Orthodox doctrine there is no middle road between God and Satan. Ultimately, and at any given moment, man is either with God or the devil, serving one or the other.
The ultimate victory belongs to God and to those with Him. Satan and his hosts are finally destroyed. Without this recognition—and still more—the experience of this reality of the cosmic spiritual struggle (God and Satan, the good angels and the evil angels), one cannot truly be called an Orthodox Christian who sees and lives according to the deepest realities of life. Once again, however, it must be clearly noted that the devil is not a “red-suited gentleman” nor any other type of grossly-physical tempter. He is a subtle, intelligent spirit who acts mostly by deceit and hidden actions, having as his greatest victory man’s disbelief in his existence and power. Thus, the devil attacks “head-on” only those whom he can deceive in no other way: Jesus and the greatest of the saints. For the greatest part of his warfare he is only too satisfied to remain concealed and to act by indirect methods and means.
Be sober, be watchful. Your adversary, the devil, prowls around like a roaring lion seeking someone to devour. (1 Pet 5:8)
Put on the whole armor of God, that you may be able to stand against the wiles of the devil. For we are not contending against flesh and blood, but against the principalities, against the powers, against the world rulers of this present darkness, against the spiritual hosts of wickedness in the heavenly places (Eph 6:11-12).
