And when I had said this I continued: I will thus prove to you therefore that the whole Psalm has been spoken of Christ, by expounding it again. When then it says at once: O God, my God, regard me; why didst Thou forsake me? this foretold of old what was to be said in the time of Christ. For when He was crucified He said: O God, O God, why didst Thou forsake me?Matthew 27:46 Mark 15:34
And the words that follow: Far from my salvation are the words of my transgressions. O my God, I will cry unto Thee by day and Thou wilt not hear, and by night, and not for lack of my understanding, were spoken in accordance with the things that He was about to do. For on the day on which He was to be crucified, He took with Him three of His disciples into the mount called the Mount of Olives, situated right opposite to the Temple in Jerusalem, and prayed, saying: Father, if it is possible, let this cup pass away from me. And afterwards He says in His prayer: Not as I desire, but as Thou wilt, making it plain by these words that He had become a man really liable to suffering.
But that none should say: He did not know then that He was to suffer, He at once brings forward in the Psalm: and not for lack of my understanding. In the same way that it was not either for lack of understanding on God’s part that He asked Adam where he was, or Cain where Abel was, but with the object that He might convince each what kind of person He was, and that the knowledge of all things should come to us through the (divine) record. So He (i.e., Christ) declared that it was not for His own lack of understanding but for that of those who supposed He was not Christ Himself, but who thought that they would put Him to death, and that He would remain in Hades as an ordinary man.