Angelic Hierarchy

Angelic Hierarchy according to St. Thomas Aquinas:


[I]t was shown above (Summa Theologiae I-I q55, a3), in treating of the angelic knowledge, that the superior angels have a more universal knowledge of the truth than the inferior angels. This universal knowledge has three grades among the angels. For the types of things, concerning which the angels are enlightened, can be considered in a threefold manner. First as preceding from God as the first universal principle, which mode of knowledge belongs to the first hierarchy, connected immediately with God, and, "as it were, placed in the vestibule of God," as Dionysius [the Areopagite] says (Coel. Hier. vii). Secondly, forasmuch as these types depend on the universal created causes which in some way are already multiplied; which mode belongs to the second hierarchy. Thirdly, forasmuch as these types are applied to particular things as depending on their causes; which mode belongs to the lowest hierarchy. [ST I-I q108, a1]

Thus does St. Thomas speak of the three-fold division of the angelic hierarchy into three hierarchies, each with three choirs of angels. In the highest hierarchy (Seraphim, Cherubim, and Thrones) the Divine Ideas take on their most universal character. Oriented immediately to God these choirs of pure spirits understand in the broadest, most general, way the knowledge committed to them by God. As the Eternal Word is the uncreated undivided Image of the Father, these angels possess the most simple, and therefore most profound, understanding of that Word, in whose image all created realities were made (Col. 1:15-17). 

In the second hierarchy (Dominions, Virtues and Powers) the Divine ideas begin to be multiplied, so as to have effect in the created universe. For St. Thomas God, the First Cause, brings about His plan for creation, except for those matters which require the divine power - such as creating out of nothing, through the secondary causation of the angels. Thus, we can say that the Divine Idea of creation and its laws, which in God is one and simple in the Eternal Word, becomes more specific and suited to material reality as it proceeds down through the angelic hierarchy. 

Finally, the lowest hierarchy (Principalities, Archangels and Angels)  understands the knowledge communicated from the higher choirs as it relates to particular realities and serves to effect in creation the will of God, such as the laws of nature, and the guardianship of societies and individuals.

St. Michael, St. Gabriel, St. Raphael (and Companions)

Sacred Scripture provides us with the names of three of the Archangels. 

Then war broke out in heaven; Michaeland his angels battled against the dragon. The dragon and its angels fought back (Rev. 12:7) [cf. Daniel 10:13, 21; 12:1; Jude 1:9]

Michael is Hebrew for Who is Like God

In the sixth month, the angel Gabriel was sent from God to a town of Galilee called Nazareth, to a virgin betrothed to a man named Joseph, of the house of David, and the virgin's name was Mary. (Luke 1:26-27) [cf. Daniel 8:16, 9:21; Luke 1:19]

Gabriel is Hebrew for Man of God, often rendered Strength of God

I am Raphael, one of the seven angels who enter and serve before the Glory of the Lord." (Tobit 12:15; cf. Tobit all]

Raphael is Hebrew for God heals

From Tobit 12:15 the Church has deduced that there are seven archangels in all. Although various ecclesiastical traditions ascribe names to the remaining four, at places such as Polermo in Sicily and St. Michael's Shrine in Tlaxcala, Mexico, these names vary from place to place and are not accepted by the Church for purposes of veneration by Catholics. Veneration of the Seven Archangels is permitted, however, and in Rome's Basilica of Our Lady of the Angels and the Jesuit church Gesu there are chapels dedicated to the 7 archangels.

The Archangels, according to Dionysius (Coel. Hier. ix), are between the Principalities and the Angels. A medium compared to one extreme seems like the other, as participating in the nature of both extremes; thus tepid seems cold compared to hot, and hot compared to cold. So the Archangels are called the "angel princes"; forasmuch as they are princes as regards the Angels, and angels as regards the Principalities. But according to Gregory (Hom. xxiv in Ev.) they are called Archangels, because they preside over the one order of the Angels; as it were, announcing greater things: and the Principalities are so called as presiding over all the heavenly "virtues" [spiritual powers, in a general sense] who fulfill the Divine commands. [ST q105, a5]

St. Thomas tells us that the Archangels bear the greatest messages of God to man. They are the chief messengers (arch-aggelos); ruling, as well, over the lesser messengers, or angels, as their chiefs. It is from this latter choir that St. Thomas asserts that the Guardian Angels of individuals are taken.