36. That the Son is the Co-existing Word, argued from the New Testament. Texts from the Old Testamentcontinued; especially Psalm 110:3. Besides, the Word in Old Testamentmay be Son in New, as Spirit in Old Testamentis Paraclete in New. Objection from Acts 10:36; answered by parallels, such as 1 Corinthians 1:5. Lev. 9:7. etc. Necessity of the Word's taking flesh, viz. to sanctify, yet without destroying, the flesh
29 Thus in the Old also, statements are plainly made concerning the Son; at the same time it is superfluous to argue the point; for if what is not stated in the Old is of later date, let them who are thus disputatious, say where in the Old is mention made of the Spirit, the Paraclete? For of the Holy Spirit there is mention, but nowhere of the Paraclete. Is then the Holy Spirit one, and the Paraclete another, and the Paraclete the later, as not mentioned in the Old? But far be it to say that the Spirit is later, or to distinguish the Holy Ghost as one and the Paraclete as another; for the Spirit is one and the same, then and now hallowing and comforting those who are His recipients; as one and the same Word and Son led even then to adoption of sons those who were worthy. For sons under the Old were made such through no other than the Son. For unless even before Mary there were a Son who was of God, how is He before all, when they are sons before Him? And how also 'First-born,' if He comes second after many? But neither is the Paraclete second, for He was before all, nor the Son later; for 'in the beginning was the Word.' And as the Spirit and Paraclete are the same, so the Son and Word are the same; and as the Saviour says concerning the Spirit, 'But the Paraclete which is the Holy Ghost, whom the Father will send in My Name,' speaking of One and Same, and not distinguishing, so John describes similarly when he says, 'And the Word became flesh, and dwelt among us, and we beheld His glory, glory as of one Only-begotten from the Father. ' For here too he does not distinguish but witnesses the identity. And as the Paraclete is not one and the Holy Ghost another, but one and the same, so Word is not one, and Son another, but the Word is Only-Begotten; for He says not the glory of the flesh itself, but of the Word. He then who dares distinguish between Word and Son, let him distinguish between Spirit and Paraclete; but if the Spirit cannot be distinguished, so neither can the Word, being also Son and Wisdom and Power. Moreover, the word 'Well-beloved' even the Greeks who are skilful in phrases know to be equivalent with 'Only-begotten.' For Homer speaks thus of Telemachus, who was the only-begotten of Ulysses, in the second book of the Odyssey:
O'er the wide earth, dear youth, why seek to run, An only child, a well-beloved son?
He whom you mourn, divine Ulysses, fell Far from his country, where the strangers dwell.
Therefore he who is the only son of his father is called well-beloved.
30. Some of the followers of the Samosatene, distinguishing the Word from the Son, pretend that the Son is Christ, and the Word another; and they ground this upon Peter's words in the Acts, which he spoke well, but they explain badly. It is this: 'The Word He sent to the children of Israel, preaching peace by Jesus Christ; this is Lord of all.' For they say that since the Word spoke through Christ, as in the instance of the Prophets, 'Thus says the Lord,' the prophet was one and the Lord another. But to this it is parallel to oppose the words in the first to the Corinthians, 'waiting for the revelation of our Lord Jesus Christ, who shall also confirm you unto the end unblameable in the day of our Lord Jesus Christ.' For as one Christ does not confirm the day of another Christ, but He Himself confirms in His own day those who wait for Him, so the Father sent the Word made flesh, that being made man He might preach by means of Himself. And therefore he straightway adds, 'This is Lord of all;' but Lord of all is the Word.
31. 'And Moses said unto Aaron, Go unto the altar and offer your sin-offering, and your burnt-offering, and make an atonement for yourself and for the people; and offer the offering of the people, and make an atonement for them, as the Lord commanded Moses.' See now here, though Moses be one, Moses himself speaks as if about another Moses, 'as the Lord commanded Moses.' In like manner then, if the blessed Peter speak of the Divine Word also, as sent to the children of Israel by Jesus Christ, it is not necessary to understand that the Word is one and Christ another, but that they were one and the same by reason of the uniting which took place in His divine and loving condescension and becoming man. And even if He be considered in two ways, still it is without any division of the Word, as when the inspired John says, 'And the Word became flesh, and dwelt among us.' What then is said well and rightly by the blessed Peter, the followers of the Samosatene, understanding badly and wrongly, stand not in the truth. For Christ is understood in both ways in Divine Scripture, as when it says Christ 'God's power and God's wisdom.' If then Peter says that the Word was sent through Jesus Christ unto the children of Israel, let him be understood to mean, that the Word incarnate has appeared to the children of Israel, so that it may correspond to 'And the Word became flesh.' But if they understand it otherwise, and, while confessing the Word to be divine, as He is, separate from Him the Man that He has taken, with which also we believe that He is made one, saying that He has been sent through Jesus Christ, they are, without knowing it, contradicting themselves. For those who in this place separate the divine Word from the divine Incarnation, have, it seems, a degraded notion of the doctrine of His having become flesh, and entertain Gentile thoughts, as they do, conceiving that the divine Incarnation is an alteration of the Word. But it is not so; perish the thought.
32. For in the same way that John here preaches that incomprehensible union. 'the mortal being swallowed up of life,' nay, of Him who is Very Life (as the Lord said to Martha, 'I am the Life '), so when the blessed Peter says that through Jesus Christ the Word was sent, he implies the divine union also. For as when a man heard 'The Word became flesh,' he would not think that the Word ceased to be, which is absurd, as has been said before, so also hearing of the Word which has been united to the flesh, let him understand the divine mystery one and simple. More clearly however and indisputably than all reasoning does what was said by the Archangel to the Bearer of God herself, show the oneness of the Divine Word and Man. For he says, 'The Holy Ghost shall come upon you, and the Power of the Highest shall overshadow you: therefore also that Holy Thing which shall be born of you, shall be called the Son of God.' Irrationally then do the followers of the Samosatene separate the Word who is clearly declared to be made one with the Man from Mary. He is not therefore sent through that Man; but He rather in Him sent, saying, 'Go, teach all nations.'
Source: Four Discourses Against the Arians (New Advent)