Our Resplendent Brothers
Archangel Gabriel fresco. Decani Monastery, Kosovo and Metohija, Serbia.
St. Nikolai (Velimirovic) opens his Alphabet of Truth with the entry about Angels:
Angels were created before men. The Book of Genesis says: In the beginning God created the heavens and the earth. Under ‘heavens’ all of God's saints have single heartedly understood angels, or the world of the divine spirits, the armies of incorporeal forces. According to the Lord's Revelation and the visions of the holy men like St. Jerotej (Hieroteos) and St. Dionysius, angels are grouped in nine orders based on the might and power and wisdom they were bestowed by the Creator. Those nine vast orders are: Seraphim, Cherubim, Thrones, Dominions, Virtues, Powers, Principalities, Archangels and Angels. Human mind cannot comprehend the magnitude and glory of the angels, nor can it calculate their numbers. Only man's heart can delight in his greater and older and superior brothers - brothers, we say, for there is one heavenly Father of both angels and men.
Note: This is my translation from Serbian, so mistakes and clumsiness are entirely mine, being that St. Nikolai's writings are graceful and refined like finely crafted jewels.