Texts Explained; Secondly, Psalm 45:7, 8.--> Whether the words 'therefore,' 'anointed,' etc., imply that the Word has been rewarded. Argued against first from the word 'fellows' or 'partakers.' He is anointed with the Spirit in His manhood to sanctify human nature. Therefore the Spirit descended on Him in Jordan, when in the flesh. And He is said to sanctify Himself for us, and give us the gloryHe has received. The word 'wherefore' implies His divinity. 'You have loved righteousness,' etc., do not imply trial or choice
48 What advancement then was it to the Immortal to have assumed the mortal? Or what promotion is it to the Everlasting to have put on the temporal? What reward can be great to the Everlasting God and King in the bosom of the Father? See ye not, that this too was done and written because of us and for us, that us who are mortal and temporal, the Lord, become man, might make immortal, and bring into the everlasting kingdom of heaven? Blush ye not, speaking lies against the divine oracles? For when our Lord Jesus Christ had been among us, we indeed were promoted, as rescued from sin; but He is the same; nor did He alter, when He became man (to repeat what I have said), but, as has been written, 'The Word of God abides for ever. ' Surely as, before His becoming man, He, the Word, dispensed to the saints the Spirit as His own, so also when made man, He sanctifies all by the Spirit and says to His Disciples, 'Receive the Holy Ghost.' And He gave to Moses and the other seventy; and through Him David prayed to the Father, saying, 'Take not Your Holy Spirit from me. ' On the other hand, when made man, He said, 'I will send to you the Paraclete, the Spirit of truth;' and He sent Him, He, the Word of God, as being faithful. Therefore 'Jesus Christ is the same yesterday, today, and for ever,' remaining unalterable, and at once gives and receives, giving as God's Word, receiving as man. It is not the Word then, viewed as the Word, that is promoted; for He had all things and has them always; but men, who have in Him and through Him their origin of receiving them. For, when He is now said to be anointed in a human respect, we it is who in Him are anointed; since also when He is baptized, we it is who in Him are baptized. But on all these things the Saviour throws much light, when He says to the Father, 'And the glory which You gave Me, I have given to them, that they may be one, even as We are one.' Because of us then He asked for glory, and the words occur, 'took' and 'gave' and 'highly exalted,' that we might take, and to us might be given, and we might be exalted in Him; as also for us He sanctifies Himself, that we might be sanctified in Him.
49. But if they take advantage of the word 'wherefore,' as connected with the passage in the Psalm, 'Wherefore God, even Your God, has anointed You,' for their own purposes, let these novices in Scripture and masters in irreligion know, that, as before, the word 'wherefore' does not imply reward of virtue or conduct in the Word, but the reason why He came down to us, and of the Spirit's anointing which took place in Him for our sakes. For He says not, 'Wherefore He anointed You in order to Your being God or King or Son or Word.' for so He was before and is for ever, as has been shown; but rather, 'Since You are God and King, therefore You were anointed, since none but You could unite man to the Holy Ghost, Thou the Image of the Father, in which we were made in the beginning; for Yours is even the Spirit.' For the nature of things originate could give no warranty for this, Angels having transgressed, and men disobeyed. Wherefore there was need of God and the Word is God; that those who had become under a curse, He Himself might set free. If then He was of nothing, He would not have been the Christ or Anointed, being one among others and having fellowship as the rest. But, whereas He is God, as being Son of God, and is everlasting King, and exists as Radiance and Expression of the Father, therefore fitly is He the expected Christ, whom the Father announces to mankind, by revelation to His holy Prophets; that as through Him we have come to be, so also in Him all men might be redeemed from their sins, and by Him all things might be ruled. And this is the cause of the anointing which took place in Him, and of the incarnate presence of the Word, which the Psalmist foreseeing, celebrates, first His Godhead and kingdom, which is the Father's, in these tones, 'Your throne, O God, is for ever and ever; a sceptre of righteousness is the sceptre of Your Kingdom;' then announces His descent to us thus, 'Wherefore God, even Your God, has anointed You with the oil of gladness above Your fellows. '
50. What is there to wonder at, what to disbelieve, if the Lord who gives the Spirit, is here said Himself to be anointed with the Spirit, at a time when, necessity requiring it, He did not refuse in respect of His manhood to call Himself inferior to the Spirit? For the Jews saying that He cast out devils in Beelzebub, He answered and said to them, for the exposure of their blasphemy, 'But if I through the Spirit of God cast out demons.' Behold, the Giver of the Spirit here says that He cast out demons in the Spirit; but this is not said, except because of His flesh. For since man's nature is not equal of itself to casting out demons, but only in power of the Spirit, therefore as man He said, 'But if I through the Spirit of God cast out demons.' Of course too He signified that the blasphemy offered to the Holy Ghost is greater than that against His humanity, when He said, 'Whosoever shall speak a word against the Son of man, it shall be forgiven him;' such as were those who said, 'Is not this the carpenter's son?' but they who blaspheme against the Holy Ghost, and ascribe the deeds of the Word to the devil, shall have inevitable punishment. This is what the Lord spoke to the Jews, as man; but to the disciples showing His Godhead and His majesty, and intimating that He was not inferior but equal to the Spirit, He gave the Spirit and said, 'Receive the Holy Ghost,' and 'I send Him,' and 'He shall glorify Me,' and 'Whatsoever He hears, that He shall speak. ' As then in this place the Lord Himself, the Giver of the Spirit, does not refuse to say that through the Spirit He casts out demons, as man; in like manner He the same, the Giver of the Spirit, refused not to say, 'The Spirit of the Lord is upon Me, because He has anointed Me,' in respect of His having become flesh, as John has said; that it might be shown in both these particulars, that we are they who need the Spirit's grace in our sanctification, and again who are unable to cast out demons without the Spirit's power. Through whom then and from whom behooved it that the Spirit should be given but through the Son, whose also the Spirit is? And when were we enabled to receive It, except when the Word became man? And, as the passage of the Apostle shows, that we had not been redeemed and highly exalted, had not He who exists in form of God taken a servant's form, so David also shows, that no otherwise should we have partaken the Spirit and been sanctified, but that the Giver of the Spirit, the Word Himself, hast spoken of Himself as anointed with the Spirit for us. And therefore have we securely received it, He being said to be anointed in the flesh; for the flesh being first sanctified in Him, and He being said, as man, to have received for its sake, we have the sequel of the Spirit grace, receiving 'out of His fullness.'
Source: Four Discourses Against the Arians (New Advent)