From The Celestial Hierarchy, ch. ix:
There remains for us the reverent contemplation of that sacred Order which completes the Angelic Hierarchies, and is composed of the Divine Principalities, Archangels and Angels.
The choir of the holy Archangels is joined with the Angels because it belongs to the interpreting Order, receiving in its turn the illuminations from the First Powers, and beneficently announcing these revelations to the Angels; and by means of the Angels it shows them forth to us in the measure of the mystical receptivity of each one who is inspired by the divine illumination. For the Angels, as we have said, fill up and complete the lowest choir of all the Hierarchies of the Celestial Intelligences since they are the last of the Celestial Beings possessing the angelic nature. And they, indeed, are more properly named Angels by us than are those of a higher rank because their choir is more directly in contact with manifested and mundane things.
The Word of God has given our hierarchy into the care of Angels, for Michael is called Lord of the people of Judah, and other Angels are assigned to other peoples. For the Most High established the boundaries of the nations according to the number of the Angels of God.
If someone should ask why the Hebrews alone were guided to the divine illuminations, we should answer that the turning away of the nations to false gods ought not to be attributed to the direct guidance of Angels, but to their own refusal of the true path which leads to God, and the falling away through self-love and perversity, and similarly, the worship of things which they regarded as divine.
For there is one Sovereign and Providence of all, and we must never suppose that God was leader of the Jews by chance, nor that certain Angels, either independently, or with equal rank, or in opposition to one another, ruled over the other nations; but this teaching must be received according to the following holy intention, not as meaning that God had shared the sovereignty of mankind with other gods, or with Angels, and had been chosen by chance as ruler and leader of Israel, but as showing that although one all-powerful Providence of the Most High consigned the whole of mankind to the care of their own Angels for their preservation, yet the Israelites, almost alone of them all, turned to the knowledge and light of the true God.
Therefore the Word of God, when relating how Israel devoted himself to the worship of the true God, says, “He became the Lord’s portion.” Moreover it shows that he too, equally with other nations, was given into the charge of one of the holy Angels, in order that he might know through him the one Principle of all things. For it says that Michael was the leader of the Jews, clearly showing that there is one Providence established superessentially above all the invisible and visible powers, and that all the Angels who preside over the different nations lift up to that Providence, as to their own Principle, as far as is in their power, those who willingly follow them.