Why does God have to sacrifice Himself?

In a conversation with Jean-Pierre Dupuy, philosopher Slavoj Zizek says the following:

“Why does God have to sacrifice himself? People usually answer me, there was sin, and sins have to be paid. No! This idea that above God there is some kind of sense of cosmic justice, that even God has to pay, is a Pagan idea. The other popular idea was that God makes a deal with the Devil.” - https://youtu.be/NEEBYNNpX9o

“Deal with the Devil” is far from a specific answer, but two excerpts from the poet William Blake offer insight to how this deal could be viewed.

“Nail his neck to the cross : nail it with a nail. / Nail his neck to the cross : ye all have power over his tail."

“What can be done with those desperate fools / Who follow after the heathen schools? / I was standing by when Jesus died. / What they called humility I called pride."

Analyzing these segments, W.B. Yeats said:

“Christ's two natures impelled Him to crucifixion. [Christ] went to ‘humble Himself to God,’ and also to proudly destroy the serpent in himself; his own spectre, or Satan. This Satan is the false (view of) Christ worshipped still.” - https://en.wikisource.org/wiki/The_works_of_William_Blake,_poetic,_symbolic_and_critical/2/The_Everlasting_Gospel

Yeats can write better than myself so I will quote him at length describing William Blake's reworking of Christian theology:

“Jehovah, in the persons of the Elohim, and by the agency of the Angel of the Divine Presence, created this dark world as an act of mercy and of cruelty. It is of mercy because it enables the weak emotions to look through symbols upon prophecy, and also because it passes away, being under Time. It is of cruelty because it cuts off joys of mind and adds on pains of mind — of that lower and shrunken part called body. It is also Satanic, because it is the region where the Accuser triumphs by means of the law which is 'the strength of sin,' as the lesson in the Anglican burial service reminds us. Satan is the Accuser. Accusation is the great mental sin. Other sin is merely physical, and belongs to the things of Time that pass. Accusation is not the only mental sin. Denial is equally deadly. Satan is not only the moral accuser but the denier of Imaginative truth, for he would have Reason and Memory only considered to be intellectual attributes. With these he builds the dark fiction of error — a belief in that delusive Goddess Nature, who is the mother of physical morality, and of mental immorality. She is Mary, the pure, and Rahab the Harlot. She is Rahab because she binds the red cord of blood in the eyes, the windows of the soul. She is Mary, because it is of that cord the red robe of flesh is made that was put on by Christ at the incarnation. Thus Mary is the greater Rahab. Rahab's harlotry is typical of mental mixture of convictions. It may be found in the physically pure. She is therefore called the Harlot-Virgin.

"The Image of God in which man was made is the form of the Imagination. This is common to all men and will end by becoming One Form. It will unite all. It will survive all... In a word it saves them from Satan, God of this world. Reason and memory tend also to unite men's personalities into one great Temporary Delusion. This is the great Satan, opposite of the great Saviour... [The great Satan] coheres by the water of death; fleshly instinct. It is bound by the fire of vegetation; fleshly growth and decay. At the incarnation Christ put on this water and this fire. The one burned the other. He ended by putting them both off. His mother was Law and Nature. His body was Satan. When crucified he was his own destroyer, destroying the Serpent in Himself. This Serpent, Satan, was what was nailed to the tree. This body was destroyed or devoured in three days. This devouring is the meaning of the serpent with his tail in his mouth. Christ's self-sacrifice (or suicide) was the thrusting into death of Satan, and who had become Himself as a result of the Incarnation. It was the eternal putting-off of Reason and Memory and Morality as delusions, that Imagination, Eternal Present, and Forgiveness might survive."

For Blake, Satan represents Error, not Sin. “Sin is to be forgiven, Error is not.”

Blake believes that we have re-created the same hypocritical system as the Pharisees that Jesus rebelled against, and, as with then, the hypocritical system is the primary source of Satan’s delusion today. Unlike in Jesus’s time, however, hypocrisy is as likely to be found in scientism as in moralism:

“I am your Rational Power O Albion & that Human Form / You call Divine, is but a Worm seventy inches long / That creeps forth in a night & is dried in the morning sun…
So spoke the Spectre to Albion. He is the Great Selfhood / Satan: Worshipd as God by the Mighty Ones of the Earth” - https://en.wikisource.org/wiki/Jerusalem._The_Emanation_of_the_Giant_Albion/Plate_33a

In short, Christ's "deal with the devil" was that rather than following the Divine order to preserve life made in the image of God, Christ acts through a healthy bodily-Satanic pride, which is of a lower order than Mind and imagination. Now, return to Blake's verse: “What can be done with those desperate fools / Who follow alter the heathen schools? / I was standing by when Jesus died. / What they called humility I called pride."

The "desperate fools" believe that Christ humbled himself before men. Blake utterly rejects this type of humility. Yeats explains: "Humility is forbidden and sinful as modesty is (which blasphemes the Symbol of God, the naked body). Humility is forbidden because it is doubt, not faith, and doubts the Godhead in ourselves, His chosen Temple... Death and Error are Reason when confined to the experience of the five senses, proud of its humility, its limits and arguments.""

The correct interpretation is that Christ humbled himself only to God, not to men. In accepting Crucifixion, Jesus was not moralistically accepting the judgment of Pilot and the pharisees. Rather, he was employing Satanic-bodily pride, parallel to the pride in his claim "And I, if I be lifted up from the earth, will draw all men unto me" (John 12:32).  Yeats explains in the higher order, 'pride' is "Elation of joy and delight in Vision," but "Healthy Satanic pride in the energy of that lower part of mind called body, has also a right to its elation because 'everything that lives is Holy'."
Christ's pride in crucifixion is Satanic because it is of his bodily, human existence, not directly related to divine Imagination.

Those who take pride in moralism and scientism are in error, because this type of pride (connected to abstract systems as opposed to Imagination or Body) necessarily leads to hypocrisy--the valuing of rules over belief.  "Death and Error are Reason when confined to the experience of the five senses, proud of its humility, its limits and arguments."