29.2. The three most ancient opinions concerning God are Anarchia, Polyarchia, and Monarchia. The first two are the playthings of the children of Hellas, and may they continue to be so. For Anarchy is a thing without order; and the Rule of Many is factious, and thus anarchical, and thus disorderly. For both these theological positions tend to the same thing, namely disorder; and thus to dissolution, for disorder is the first step to dissolution. But Monarchy is that axiom which we hold in honor. It is, however, a Monarchy that is not limited to one person, for it is possible for unity, if at variance with itself, to come into a condition of plurality; but we hold it to be made out of an equality of nature and a union of mind, and an identity of motion, and a consilience of its elements to unity (a thing which is impossible for created natures) so that though it is numerically distinct there is no severance of essence involved. Therefore Unity having from all eternity arrived by motion at Duality, found its rest in Trinity. This is what we mean by Father and Son and Holy Spirit. The Father is the Begetter and the Emitter; though without passion, of course, and without reference to time, and not in a corporeal manner. The Son is the Begotten, and the Holy Spirit the Emission; (I say this since I do not know how else this can be expressed in terms that wholly exclude material conceptions). But we shall not venture to speak of “An overspill of goodness,” as one of the Greek Philosophers dared to say, as if God were like a wine-bowl filled to overflowing, saying this in plain words in his oration on the First and Second Causes. Let us never look on this matter of divine generation as being involuntary, like some natural overflow, hard to be retained, for it is by no means fitting to our conception of the Godhead. Therefore let us confine ourselves within our proper limits, and speak of the “Unbegotten” and the “Begotten” and that which “Proceeds from the Father,” as in one place God the Word himself expressed it.
Oration 29 as reproduced in The Encyclopedia of Eastern Orthodox Christianity, 699.