Athanasius Ad Ser., 1:17, 20

17. For this reason too, it is madness to call him a creature. If he were a creature, he would not be ranked with the Triad. For the whole Triad is one God. It is enough to know that the Spirit is not a creature, nor is he numbered with the things that are made. For nothing foreign is mixed with the Triad; it is indivisible and consistent. These things are sufficient for the faithful. Thus far human knowledge goes. Here the cherubim spread the covering of their wings. He who seeks and would inquire into what lies beyond these things disobeys him who said: ‘Be not wise in many things, lest thou be confounded.’ For the things that have been handed down by faith ought not to be measured by human wisdom, but by the hearing of faith. What speech shall be able worthily to interpret the things that surpass originated nature? Or what hearing is able to understand things it is not lawful for men either to hear or to utter ? For that is how Paul spoke of what he heard ; but of God himself, ‘How are his ways past tracing out !’, and, ‘Who hath known the mind of the Lord and who hath been his counsellor?’ Abraham was not a busybody, nor did he question him who spoke, but believed and ‘it was counted to him for righteousness’. Thus Moses was called ‘a faithful servant’. But if the disciples of Arius, because wisdom will not enter their deceitful hearts, are not able intelligently to believe in the indivisible and holy Triad, let them not on that account pervert the truth as well, neither let them say that what they cannot understand cannot be true. They have put themselves in an absurd position. Because they cannot understand how the holy Triad is indivisible, the Arians make the Son one with the creation, and the Tropici, for their part, number the Spirit with the creatures. It would be better for them either to say nothing at all in their incomprehension, the Arians not ranking the Son with the creatures nor the Tropici the Spirit; or else to acknowledge what is written, and join the Son to the Father and not divide the Spirit from the Son — so that the Holy Triad may still be rightly characterized as indivisible and of one nature. Having learned these truths, they ought not to be so bold as to ask doubting, how these things could be; lest, even if he whom they question be at a loss for words, of their own accord they think out false notions for themselves. For all created beings, and especially we who are men, find it impossible to speak adequately concerning the things that are ineffable. All the more presumptuous, then, if, when we cannot speak, we devise for these subjects strange forms of expression other than those in the Scriptures. Above all is this present attempt madness, both on the part of him who asks and of him who so much as thinks of answering. For he who asked such questions even about originated things would not be regarded as of sound mind.

20. But if there is such co-ordination and unity within the holy Triad, who can separate either the Son from the Father, or the Spirit from the Son or from the Father himself? Who would be so audacious as to say that the Triad is unlike itself and diverse in nature, or that the Son is in essence foreign from the Father, or the Spirit alien from the Son? But how are these things? If one should make inquiry and ask again : How, when the Spirit is in us, the Son is said to be in us ? How, when the Son is in us, the Father is said to be in us? Or how, when it is truly a Triad, the Triad is described as one? Or why, when the One is in us, the Triad is said to be in us? — let him first divide the radiance from the light, or wisdom from the wise, or let him tell how these things are. But if this is not to be done, much more is it the audacity of madmen to make such inquiries concerning God. For tradition, as we have said, does not declare the Godhead to us by demonstration in words, but by faith and by a pious and reverent use of reason. For if Paul proclaimed the saving Gospel of the Cross, ‘not in words of wisdom, but in demonstration of the Spirit and of power’; and if in Paradise he heard ‘unspeakable words which it is not lawful for a man to utter’: who can declare the holy Triad itself? Nevertheless, we can meet this difficulty, primarily by faith and then by using the illustrations mentioned above, I mean the image and the radiance, fountain and river, essence and expression. As the Son is in the Spirit as in his own image, so also the Father is in the Son. For divine Scripture, by way of relieving the impossibility of explaining and apprehending these matters in words, has given us illustrations of this kind; that it may be lawful, because of the unbelief of presumptuous men, to speak more plainly, and to speak without danger, and to think legitimately, and to believe that there is one sanctification, which is derived from the Father, through the Son, in the Holy Spirit.

As the Son is an only-begotten offspring, so also the Spirit, being given and sent from the Son, is himself one and not many, nor one from among many, but Only Spirit. As the Son, the living Word, is one, so must the vital activity and gift whereby he sanctifies and enlightens be one perfect and complete; which is said to proceed from the Father, because it is from the Word, who is confessed to be from the Father, that it shines forth and is sent and is given. The Son is sent from the Father; for he says, ‘God so loved the world that he gave his only begotten Son.’ The Son sends the Spirit; ‘If I go away,’ he says, ‘I will send the Paraclete.’ The Son glorifies the Father, saying: ‘Father, I have glorified thee.’ The Spirit glorifies the Son; for he says: ‘He shall glorify me.’ The Son says: ‘The things I heard from the Father speak I unto the world.’ the Spirit takes of the Son; ‘He shall take of mine,’ he says, ‘and shall declare it unto you.’ The Son came in the name of the Father. ‘The Holy Spirit,’ says the Son, ‘whom the Father will send in my name.’