The Word is a Substantive Being
For you will say, what is a word, but a voice and sound of the mouth, and air when struck against, intelligible to the ear, but for the rest a sort of void, empty, and incorporeal thing. I, on the contrary, contend that nothing empty and void could have come forth from God, seeing that it is not put forth from that which is empty and void; nor could that possibly be devoid of substance which has proceeded from so great a substance, and has produced such mighty substances: for all things which were made through Him, He Himself (personally) made. How could it be, that He Himself is nothing, without whom nothing was made? How could He who is empty have made things which are solid, and He who is void have made things which are full, and He who is incorporeal have made things which have body?
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For who will deny that God is a body, although “God is a Spirit?” For Spirit has a bodily substance of its own kind, in its own form. Now, even if invisible things, whatsoever they be, have both their substance and their form in God, whereby they are visible to God alone, how much more shall that which has been sent forth from His substance not be without substance! Whatever, therefore, was the substance of the Word that I designate a Person, I claim for it the name of Son; and while I recognize the Son, I assert His distinction as second to the Father.
— Against Praxeas VII
The Unity of the Father and the Son
The Son alone knows the Father, and has Himself unfolded “the Father’s bosom.” He has also heard and seen all things with the Father; and what He has been commanded by the Father, that also does He speak. And it is not His own will, but the Father’s, which He has accomplished, which He had known most intimately, even from the beginning. “For what man knoweth the things which be in God, but the Spirit which is in Him?” But the Word was formed by the Spirit, and (if I may so express myself) the Spirit is the body of the Word. The Word, therefore, is both always in the Father, as He says, “I am in the Father” and is always with God, according to what is written, “And the Word was with God” and never separate from the Father, or other than the Father, since “I and the Father are one.” This will be the prolation, taught by the truth, the guardian of the Unity, wherein we declare that the Son is a prolation from the Father, without being separated from Him. For God sent forth the Word, as the Paraclete also declares, just as the root puts forth the tree, and the fountain the river, and the sun the ray.
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Everything which proceeds from something else must needs be second to that from which it proceeds, without being on that account separated. Where, however, there is a second, there must be two; and where there is a third, there must be three. Now the Spirit indeed is third from God and the Son; just as the fruit of the tree is third from the root, or as the stream out of the river is third from the fountain, or as the apex of the ray is third from the sun. Nothing, however, is alien from that original source whence it derives its own properties.
— Against Praxeas VIII