And again Isaiah the prophet says:
Thus saith the Lord God to my Anointed the Lord, whose right hand I have held, that the Gentiles should hearken before him. And how the Christ is called Son of God and King of the Gentiles, that is, of all mankind; and that He not only is called but is Son of God and King of all, David declares thus:
The Lord said unto me: Thou art any Son, this day have I begotten thee. Ask of me and I will give thee the Gentiles for thy inheritance, and for a possession the utmost parts of the earth. These things were not said of David; for neither over the Gentiles nor over the utmost parts did he rule, but only over the Jews. So then it is plain that the promise to the Anointed to reign over the utmost parts of the earth is to the Son of God, whom David himself acknowledges as his Lord, saying thus:
The Lord said unto my Lord, Sit on my right hand, and so forth, as we have said above. For he means that the Father speaks with the Son; as we showed a little before as to Isaiah, that he said thus:
God saith to my Anointed the Lord, that the Gentiles should hearken before him. For the promise is the same by the two prophets, that He should be King: so that the speech of God is addressed to one and the same, I mean, to Christ the Son of God. Forasmuch as David says:
The Lord said unto me, it is necessary to say that it is not David who speaks, nor any one of the prophets, in his own person: for it is not a man who speaks the prophecies; but the Spirit of God, assimilating and likening Himself to the persons represented, speaks in the prophets, and utters the words sometimes from Christ and sometimes from the Father.