9 But it may well excite a question, in what sense they were styled (Christs, or) anointed, before there was any unction, from which this title was given to the kings....Whence then were those patriarchs at that time called “anointed”? For that they were prophets, we read concerning Abraham; and certainly, what is manifestly said of him, should be understood of them also. Are they styled “christs,” because, even though secretly, yet they were already Christians? For although the flesh of Christ came from them, nevertheless Christ came before them; for He thus answered the Jews, “Before Abraham was, I am.” But how could they not know Him, or not believe in Him; since they are called prophets for this very reason, because, though somewhat darkly, they announced the Lord beforehand? Whence He says Himself openly, “Your father Abraham desired to see My day, and he saw it, and was glad.” For no man was ever reconciled unto God outside of that faith which is in Christ Jesus, either before His Incarnation, or after: as it is most truly defined by the Apostle: “For there is one God, and one Mediator between God and men, the Man Christ Jesus.”
Source: The Enarrations, or Expositions, on the Psalms (New Advent)