The ANGELS are the lowest of all the orders in the heavenly hierarchy and the closest to man. They announce the lesser mysteries and intentions of God and teach people to live virtuously and righteously before God. They are appointed to guard each of us who believe: they sustain virtuous people from fallen, and never leave us though we have sinned, but are always ready to help us, if only we ourselves want it. All of the heavenly orders are also called by the common name " angels". Although they have different names according to their situation and grace given by God (as seraphim, cherubim, thrones and the rest of the orders), yet all in general are called angels, because the word "angel" is not a denomination of essence, but of service, as it is written: "Are they not all ministering spirits, sent forth to minister" (Heb. 1:14). But their service is different and not identical: each order has its own service; for the All-Wise Creator does not reveal the mystery of His design to all to the same degree, but from the one to the others, through the higher He enlightens the lower, revealing to them His will and commanding it to be as in the book of the Prophet Zachariah. There it is said that one angel, after conversing with the prophet, met another angel who ordered him to go again to the prophet and reveal the future fate of Jerusalem: "And behold, the angel that talked with me went forth and another angel went out to meet him, and said unto him, Run, speak to this young man (that is, the prophet Zachariah), saying, Jerusalem shall be inhabited as towns without walls for the multitude of men and cattle therein: For I, saith the Lord will be unto her a wall of fire round about" (Zach. 2:3-5).
Deliberating about this, St. Gregory the Dialogist says, "When one angel says to the other: 'Run speak to this young man' there is no doubt that certain angels send others, that the lower ones are sent, that the higher send" (St. Gregory the Dialogist, Interpretation of the Gospels, #4).
We find exactly the same thing in the prophecy of Daniel, that one angel orders another to interpret the vision to the prophet. From this it is evident that angels of higher orders reveal the divine will and intention of their Creator to angels of the lower orders, that they enlighten them and send them to people. The Orthodox Church militant, being in need of the help of the angels, celebrates the Assembly of all the nine angelic orders with a special supplication, as is fitting, on the eighth day of the month of November (Nov. 21,OS) i.e. the ninth month, since all these nine orders of angels will gather on the day of the Terrible Judgment of the Lord, which the divine teachers of the Church call the eighth day. For they say, at the end of seven thousand years will begin as if an eighth day, "When the Son of man shall in His glory, and all the holy angels with Him" (as the Lord Himself foretold in the Gospel.)
From the Minea of St. Dimitry of Rostov