"My God, my God why have you forsaken me".
Why does the Lord make this cry from the Cross?
It is a quotation from Psalm 22, it begins with emptiness but actually ends in triumph. Nevertheless the words that Jesus chooses to quote are barren and bleak.
The whole process of crucifixion, and one may suspect Jesus' crucifixion especially, was to turn him into a "man despised and rejected" in the eyes of the population, and in his own eyes to become a "worm and no man". It was not just the physical destruction of Jesus that was desired but his annihilation in every way. The one who claimed equality with God has to be reduced to less than nothingness. It is part of Divine humility that the Son of God should place himself under mankind, not merely taking on death but in a sense placing himself under death itself, hence the dreadfulness of his death.
Some have suggested that this cry is really a loss of faith on Jesus' part, that sees his mission turned to nothingness, that his Father really has deserted him. I am inclined to agree to a point. The humiliation of Jesus is one suspects only partially described in the Gospels. We are left to imagine quite what his torturers actually did in darkness of the Praetorium it can only be seen by the darkness of the human soul, Roman torturers were as professional as their modern brothers and knew how to make a man confess, to break him, or to reduce him to whatever the chose. It presumably wasn't just physical pain but psychological and emotional pain they could inflict. Crucifixion is a terrible death but there are worst deaths, Jesus' death is not merely about the visible suffering and the destruction of his body but the disintegration of his very being.
Jesus in his humanity is a the Man of Faith.
How does he know he is the Son of God? Surely in the same way that we know are by adoption sons (or daughters) of God, it is by Faith, that is how human beings relate to God. To suggest anything else would be to suggest that Jesus was hybrid God-Man, and therefore a denial of the most essential Christological doctrines.
During his life, like us, he experienced moments of deep contemplative intimacy, perfect union with God, at times like the Transfiguration or Baptism, times when faith gives way to absolute certainty, in human terms, when the veil of human limitation dissolves and there is perfect and intimate knowledge. As Catholics we have to believe that Jesus has before him the Beatific Vision always. It is legitimate to ask, how he had it. The struggle in Gethsemane would suggest that it was by subjecting his human will to the Divine will, this was obviously no painless experience. We humans want to flee death and pain, it is our nature but Jesus' will is to conform his humanity (and ours) to that of the Father, in that sense "he learns obedience through suffering".
I don't think this is heresy but it seems that at the end in Jesus all that existed was faith, all that might have sustained his relationship with the Father is gone, miracles are gone, prophecy is gone, the sense of delight in God has gone, there is no sense of the Presence of God, or even his comfort. Hence Jesus by pure and perfect faith in absolute desolation, cries out, "My God, my God". This is perfect obedience, what our first parents lost by seeking knowledge, Jesus restores by the absolute pain of the loss of knowledge, the absence of any comprehension of God, in total human misery and alienation.
His faith exists when everything else that leads him to feel or experience God is absent. This is the Divine Dark Night of the Soul when everything dissolves except God, even Jesus' human image and understanding or intuition of God. The immensity of Jesus capacity and yearning for God is drained, empty, dried up, he thirsts, for mankind but infinitely more so for God. There is no vision, only darkness and emptiness and numbness.
Jesus in his perfect humanity stands face to face with God in uncomprehending comprehension abandons himself to God. There is nothing left but Faith, the Union of God and Man and nothing in the desolation of the Cross to support Faith but Faith, itself and in the emptiness of the Faith absolute Divine Love and resignation to the Will of God. There is nothing left but for Jesus to place himself into the hands of the Father in the darkness of his pain a alienation.
This is the supreme act of divine kinosis, Jesus breathing forth his Spirit into the Eternal emptiness and darkness of God and in so doing he fills and enlightens humanity's with His Spirit.