But our argument in reply to this is ready and clear. For any one who condemns those who say that the Godhead is one, must necessarily support either those who say that there are more than one, or those who say that there is none. But the inspired teaching does not allow us to say that there are more than one, since, whenever it uses the term, it makes mention of the Godhead in the singular; as “In Him dwells all the fullness of the Godhead Colossians 2:9”; and, elsewhere “The invisible things of Him from the foundation of the world are clearly seen, being understood by the things that are made, even His eternal power and Godhead Romans 1:20.” If, then, to extend the number of the Godhead to a multitude belongs to those only who suffer from the plague of polytheistic error, and on the other hand utterly to deny the Godhead would be the doctrine of atheists, what doctrine is that which accuses us for saying that the Godhead is one? But they reveal more clearly the aim of their argument. As regards the Father, they admit the fact that He is God , and that the Son likewise is honoured with the attribute of Godhead; but the Spirit, Who is reckoned with the Father and the Son, they cannot include in their conception of Godhead, but hold that the power of the Godhead, issuing from the Father to the Son, and there halting, separates the nature of the Spirit from the Divine glory. And so, as far as we may in a short space, we have to answer this opinion also.
What, then, is our doctrine? The Lord, in delivering the saving Faith to those who become disciples of the word, joins with the Father and the Son the Holy Spirit also; and we affirm that the union of that which has once been joined is continual; for it is not joined in one thing, and separated in others. But the power of the Spirit, being included with the Father and the Son in the life-giving power, by which our nature is transferred from the corruptible life to immortality, and in many other cases also, as in the conception of “Good,” and “Holy,” and “Eternal,” “Wise,” “Righteous,” “Chief,” “Mighty,” and in fact everywhere, has an inseparable association with them in all the attributes ascribed in a sense of special excellence. And so we consider that it is right to think that that which is joined to the Father and the Son in such sublime and exalted conceptions is not separated from them in any.
Read it carefully and read it all.