In what manner in the confession of the three hypostases we preserve the pious dogma of the Monarchia. Wherein also is the refutation of them that allege that the Spirit is subnumerated.
44. In delivering the formula of the Father, the Son, and the Holy Ghost, our Lord did not connect the gift with number. He did not say “into First, Second, and Third,” nor yet into one, two, and three, but He gave us the boon of the knowledge of the faith which leads to salvation, by means of holy names. So that what saves us is our faith. Number has been devised as a symbol indicative of the quantity of objects. But these men, who bring ruin on themselves from every possible source, have turned even the capacity for counting against the faith. Nothing else undergoes any change in consequence of the addition of number, and yet these men in the case of the divine nature pay reverence to number, lest they should exceed the limits of the honour due to the Paraclete. But, O wisest sirs, let the unapproachable be altogether above and beyond number, as the ancient reverence of the Hebrews wrote the unutterable name of God in peculiar characters, thus endeavouring to set forth its infinite excellence. Count, if you must; but you must not by counting do damage to the faith. Either let the ineffable be honoured by silence; or let holy things be counted consistently with true religion. There is one God and Father, one Only-begotten, and one Holy Ghost. We proclaim each of the hypostases singly; and, when count we must, we do not let an ignorant arithmetic carry us away to the idea of a plurality of Gods.
45. For we do not count by way of addition, gradually making increase from unity to multitude, and saying one, two, and three—nor yet first, second, and third. For “I,” God, “am the first, and I am the last.” And hitherto we have never, even at the present time, heard of a second God. Worshipping as we do God of God, we both confess the distinction of the Persons, and at the same time abide by the Monarchy. We do not fritter away the theology in a divided plurality, because one Form, so to say, united in the invariableness of the Godhead, is beheld in God the Father, and in God the Only begotten. For the Son is in the Father and the Father in the Son; since such as is the latter, such is the former, and such as is the former, such is the latter; and herein is the Unity. So that according to the distinction of Persons, both are one and one, and according to the community of Nature, one. How, then, if one and one, are there not two Gods? Because we speak of a king, and of the king's image, and not of two kings. The majesty is not cloven in two, nor the glory divided. The sovereignty and authority over us is one, and so the doxology ascribed by us is not plural but one; because the honour paid to the image passes on to the prototype. Now what in the one case the image is by reason of imitation, that in the other case the Son is by nature; and as in works of art the likeness is dependent on the form, so in the case of the divine and uncompounded nature the union consists in the communion of the Godhead. One, moreover, is the Holy Spirit, and we speak of Him singly, conjoined as He is to the one Father through the one Son, and through Himself completing the adorable and blessed Trinity. Of Him the intimate relationship to the Father and the Son is sufficiently declared by the fact of His not being ranked in the plurality of the creation, but being spoken of singly; for he is not one of many, but One. For as there is one Father and one Son, so is there one Holy Ghost. He is consequently as far removed from created Nature as reason requires the singular to be removed from compound and plural bodies; and He is in such wise united to the Father and to the Son as unit has affinity with unit.
46. And it is not from this source alone that our proofs of the natural communion are derived, but from the fact that He is moreover said to be “of God;” not indeed in the sense in which “all things are of God,” but in the sense of proceeding out of God, not by generation, like the Son, but as Breath of His mouth. But in no way is the “mouth” a member, nor the Spirit breath that is dissolved; but the word “mouth” is used so far as it can be appropriate to God, and the Spirit is a Substance having life, gifted with supreme power of sanctification. Thus the close relation is made plain, while the mode of the ineffable existence is safeguarded. He is moreover styled 'Spirit of Christ,' as being by nature closely related to Him. Wherefore “If any man have not the Spirit of Christ, he is none of His.” Hence He alone worthily glorifies the Lord, for, it is said, “He shall glorify me,” not as the creature, but as “Spirit of truth,” clearly showing forth the truth in Himself, and, as Spirit of wisdom, in His own greatness revealing “Christ the Power of God and the wisdom of God.” And as Paraclete He expresses in Himself the goodness of the Paraclete who sent Him, and in His own dignity manifests the majesty of Him from whom He proceeded. There is then on the one hand a natural glory, as light is the glory of the sun; and on the other a glory bestowed judicially and of free will ' ab extra' on them that are worthy. The latter is twofold. “A son,” it is said, “honours his father, and a servant his master.” Of these two the one, the servile, is given by the creature; the other, which may be called the intimate, is fulfilled by the Spirit. For, as our Lord said of Himself, “I have glorified You on the earth: I have finished the work which you gave me to do;” so of the Paraclete He says “He shall glorify me: for He shall receive of mine, and shall show it unto you.” And as the Son is glorified of the Father when He says “I have both glorified it and will glorify it again,” so is the Spirit glorified through His communion with both Father and Son, and through the testimony of the Only-begotten when He says “All manner of sin and blasphemy shall be forgiven unto men: but the blasphemy against the Holy Ghost shall not be forgiven unto men.”
47. And when, by means of the power that enlightens us, we fix our eyes on the beauty of the image of the invisible God, and through the image are led up to the supreme beauty of the spectacle of the archetype, then, I ween, is with us inseparably the Spirit of knowledge, in Himself bestowing on them that love the vision of the truth the power of beholding the Image, not making the exhibition from without, but in Himself leading on to the full knowledge. “No man knows the Father save the Son.” And so “no man can say that Jesus is the Lord but by the Holy Ghost.” For it is not said through the Spirit, but by the Spirit, and “God is a spirit, and they that worship Him must worship Him in spirit and in truth,” as it is written “in your light shall we see light,” namely by the illumination of the Spirit, “the true light which lights every man that comes into the world.” It results that in Himself He shows the glory of the Only begotten, and on true worshippers He in Himself bestows the knowledge of God. Thus the way of the knowledge of God lies from One Spirit through the One Son to the One Father, and conversely the natural Goodness and the inherent Holiness and the royal Dignity extend from the Father through the Only-begotten to the Spirit. Thus there is both acknowledgment of the hypostases and the true dogma of the Monarchy is not lost. They on the other hand who support their sub-numeration by talking of first and second and third ought to be informed that into the undefiled theology of Christians they are importing the polytheism of heathen error. No other result can be achieved by the fell device of sub-numeration than the confession of a first, a second, and a third God. For us is sufficient the order prescribed by the Lord. He who confuses this order will be no less guilty of transgressing the law than are the impious heathen.
Source: De Spiritu Sancto (New Advent)