The trial of Christ. Why?
Have you ever stopped to think why Jesus needed to be tried by the Sanhedrin, Pilate and Herod? Why couldn't he, for example, have cried out in the Garden, "I'm ready. Punish me now." What do the trial narratives add to the theology of this moment (aside from the obvious fact that they are describing historically what happened)? I think it works on a number of levels.
To display Jesus' perfection
The injustice of the trial scenes reinforce Jesus innocence and perfection. True, you would see this otherwise from the Gospel accounts themselves, but the injustice of the trials and the system makes the perfection of Christ stand out in stark relief. "He who knew no sin became sin for us, that in him we might become the righteousness of God."
To explain Jesus' substitution
This last verse (2 Cor 5.21) introduces another idea which is graphically displayed in the trial accounts - that of substitution. All the gospels include Barabbas in their description of the kangaroo court. He is a guilty man, deserving of the punishment he is about to suffer. Yet Jesus takes his place. The guilty man is released, the Innocent is punished in his place. Although most modern translations are very reluctant indeed to translate it, Matthew actually records the insurrectionists name as "Jesus Barabbas" (in Matt 27.16, the Committee on Bible translation couldn't agree on this inclusion, but the MS it occurs in are all very old).
To model Jesus' forbearance
In all the discussion about penal substitutionary atonement, it is sometimes forgotten that the suffering of Christ is held up as an example to Christians - see 1 Peter 2.21-25. We too should be prepared to suffer unjustly for the sake of the cross. (It is interesting to see that Peter takes the exemplary aspect of Jesus' suffering and allows it to take him to substitutionary atonement anyway - in 1 Peter 2.24).

