From the very beginning of man, we have heard about Angels. God placed a Cherubim with a flaming sword to guard the entrance to Paradise (Gen. 3:24); Jacob saw Angels in his vision (Gen. 23:12); and later, in Genesis 32.1-2, in Psalms (148:2 and 90:11) Prophet Isaiah saw Seraphim surrounding the Throne of God and Prophet Ezekiel saw Cherubim in his vision of the House of God.
The New Testament also contains many references to angelic beings.
"Zacharias saw him... I am Gabriel, that stands in the presence of God; I am sent to speak unto thee and to show thee glad tidings. " Luke 1:11, 12 & 19
As far as is known, the Angels are divided into nine ranks. Angels, Archangels, Powers, Authorities, Principalities, Dominions, Thrones, Cherubim and Seraphim.
Apostle Paul, in his Epistle to the Colossians, writes,
"By Him were all things created that are in Heaven and that are on earth, visible and invisible, whether, Thrones or Dominions, or Principalities or Powers" (Col. 1-16).
The high-ranking Angels' names are revealed in the Scriptures; seven are known to us. Michael, "Who is Like God" (Dan. 10.13); Gabriel, "Man of God" (Luke 1.19 & 26). Three Angels are mentioned in the non-canonical books, Raphael, "The Help of God" (Tobit, 3.17, 12.12-15); Uriel, "The Fire of God" (III Esdras 4.1, 5.20); and Salathiel, "Prayer of God" (III Esdras 5.16). The other two are Jegudiel. "Praise of God" and Barachiel, "Blessing of God".
Apostle John the Theologian, in the Apocalypse, states,
"Grace be unto you and peace from Him, which is, and which was, and which is to come, and from the seven spirits which are before His Throne" (Apoc. 1.4).
As to the question of the number of angelic beings that exist, Prophet Daniel in his vision, tells us that "Thousand thousands ministered unto Him and ten thousand times ten thousand stood before Him" (Dan. 7.10), St.Cyril of Jerusalem says that, in comparison with the number of men who had lived on earth from the time of Adam, the count of Angels was much, much greater.
Angels are the most perfect spirits. They surpass man by their spiritual powers: however, they also are created beings and bear in themselves the seal of limitations. Being without flesh, they can pass through vast space with extreme speed.
Within the Sacred Scriptures we read of Angels descending to earth. It is understood that Angels are immortal and that they cannot die (Luke 20.36). Their immortality is not divine immortality, like that of God; they have been created before our earth came into existence.
"When the stars were made, all my Angels praised Me with a loud voice", said the Lord to Job (Job 38.7).
Angels are active spirits with intelligence, knowledge and a will of their own - servants of God. The fulfillers of His providential will, they glorify God.
Angels do not appear to us exactly as they are, but as God wills them to appear. They appear in so many different forms as described by their beholders.
The Angels were ordained by God to be the most perfect reflection of His grandeur and glory. The Angels sing glory to God. Some stand before Him. St.Gregory the Theologian, in Homily 6, writes that the Angels are appointed for the "governance of the elements and the heavens, the world and everything that is in it."
There are the same number of the "fallen Angels" on the darker side. For when they split, the Bible tells us that they were divided into equal numbers. Those dark angelic beings and forces are without ceasing at work on mankind, attempting to confuse and to deceive man's belief in God and the Lord Jesus Christ. They are working on human weaknesses so as to corrupt and drag humanity to its lowest ebb.
from Orthodox Dogmatic Theology