II. Christ's death was voluntary on His part, and yet in saving others He could not save Himself
Jesus, therefore, cried with a loud voice, saying, “Why have You forsaken Me?” in order to notify to all how it behooved Him not to be rescued, not to be defended, but to be given up into the hands of cruel men, that is to become the Saviour of the world and the Redeemer of all men, not by misery but by mercy; and not by the failure of succour but by the determination to die. But what must we feel to be the intercessory power of His life Who died and rose again by His own inherent power. For the blessed Apostle says the Father “spared not His own Son, but gave Him up for us all;” and again, he says, “For Christ loved the Church, and gave Himself up for her, that He might sanctify it.”
And hence the giving up of the Lord to His Passion was as much of the Father's as of His own will, so that not only did the Father “forsake” Him, but He also abandoned Himself in a certain sense, not in hasty flight, but in voluntary withdrawal. For the might of the Crucified restrained itself from those wicked men, and in order to avail Himself of a secret design, He refused to avail Himself of His open power. For how would He who had come to destroy death and the author of death by His Passion have saved sinners, if he had resisted His persecutors?
This, then, had been the Jews' belief, that Jesus had been forsaken by God, against Whom they had been able to commit such unholy cruelty; for not understanding the mystery of His wondrous endurance, they said in blasphemous mockery: “He saved others, Himself He cannot save. If He be the King of Israel, let Him now come down from the cross, and we believe Him.” Not at your blind will, O foolish scribes and wicked priests, was the Saviour's power to be displayed, nor in obedience to blasphemers' evil tongues was the Redemption of mankind to be delayed; for if you had wished to recognize the Godhead of the Son of God, you would have observed His numberless works, and they must have confirmed you in that faith, which you so deceitfully promise.
But if, as you yourselves acknowledge, it is true that He saved others, why have those many, great miracles, which have been done under the public gaze, done nothing to soften the hardness of your hearts, unless it be because you have always so resisted the Holy Ghost as to turn all God's benefits towards you into your destruction? For even though Christ should descend from the cross, you would yet remain in your crime.
Source: Sermons (New Advent)