Jürgen Moltmann's The Crucified God: The Cross of Christ as the Foundation and Criticism of Christian Theology is one of the greatest theology books every published on the crucifixion of Jesus Christ, and an excellent book to read today on Good Friday. Moltmann argues that the theology of the cross (theologia crucis) is the reverse side of the theology of hope (eschatologia crucis), and the two are inseparable:

"For me, however, this is not a step back from the trumps of Easter to the lamentations of Good Friday. As I intend to show, the theology of the cross is none other than the reverse side of the Christian theology of hope, if the starting point of the latter lies in the resurrection of the crucified Christ." [1]

Moltmann unites Good Friday and Easter by the Silence that stands between these two events. The crucifixion and resurrection of Jesus Christ are one unified event, despite the span of time between these two events they are one indivisible event: "the resurrection of the crucified Christ" (as Moltmann said). 

"Here we come to matters about which the Easter faith says nothing. No witnesses claims to have seen what happened between Good Friday and Easter. There are no eye-witnesses to the process of resurrection of Jesus from the tomb." [p169]

The genius of Moltmann's Crucified God and specifically his contributions to understanding the silence between the theology of the cross and a theology of hope. There is no resurrection without the crucifixion of Jesus, and so the revelation of Jesus Christ as the son of God in power is only possible through the abandonment of Jesus Christ on the cross. And in order to fully understand the abandonment of Jesus, we must understand the Jesus as the crucified God.  

"How is this Easter day fellowship of God with God to be conceived in the Good Friday cross? To comprehend God in the crucified Jesus, abandoned by God, requires a 'revolution in the concept of God'." [p153] 

Moltmann argues that the revolution necessitates embracing patripassianism, and fully embracing Jesus Christ as the "Crucified God". In order to fully embrace Good Friday, and understand the ramifications of Jesus Christ's death on the cross, necessitates the belief that God has died on the cross in Jesus Christ. If God cannot experience human suffering and abandonment, how may God ever love humanity?

In fine print, Moltmann does not require the completely embrace of patripassianism because of its link to the heresiarch Sabellius. Moltmann argues that the Father does not suffer in the same way as Jesus, so some nuance of terms is required, but if God cannot suffer, then how is it true to say that God is love or loves humanity?

"We cannot therefore say here in patripassian terms that the Father also suffered and died. The suffering and dying of the son, forsaken by the Father, is a different kind of suffering from the suffering of the Father in the death of the Son." [p243]

Moltmann uses a quotation from Elie Wiesel's Night to explain his theology of the cross. Whenever we experience the most horrific suffering, we may think of Jesus Christ crucified on the cross (especially on Good Friday), and know that whatever horror we have experience, Jesus the son of God has also experienced it in his crucifixion; and whenever we experience suffering, we may remember that Jesus is there with us, asking the same question "Where is God?" in our suffering. 

A shattering expression of the theologia crucis (Theology of the Cross) which is suggested in the rabbinic theology of God’s humiliation of himself is to be found in Night, a book written by E. Wiesel, a survivor of Auschwitz:

The SS hanged two Jewish men and a youth in front of the whole camp. The men died quickly, but the death throes of the youth lasted for half an hour. ‘Where is God? Where is he?’ someone asked behind me. As the youth still hung in torment in the noose after a long time, I heard the man call again, ‘Where is God now?’ And I heard a voice in myself answer: ‘Where is he? He is here. He is hanging there on the gallows . . .’

Any other answer would be blasphemy. There cannot be any other Christian answer to the question of this torment. To speak here of a God who could not suffer would make God a demon. To speak here of an absolute God would make God an annihilating nothingness. To speak here of an indifferent God would condemn men to indifference. [1]

In addition to this quotation from Night in the Crucified God, Moltmann wrote a personal letter to my friend encouraging him (and us) to read Endo's Silence as well (the Silence movie is excellent as well). Also, I highly recommend reading the Moltmanniac's commentary on Moltmann and Elie Wiesel's Night.

Moltmann often says we do not know why there is suffering in the world, but the answer to suffering is the resurrection of the crucified God. So, we may hope for the resurrection for the entire world. 

Sources:

1. Jurgen Moltmann, The Crucified God: The Cross of Christ as the Foundation and Criticism of Christian Theology, p5

2. Moltmann. Ibid. p. 169

3. Moltmann. Ibid. p. 153

4. Moltmann. Ibid. p. 243

4. Moltmann. Ibid. p. 273-274