I think there are three ways into this question, and I'll take them in turn.
The suffering of Jesus is a pivotal event in the moral order of things. When, in the ordinary course of our lives, we consider something awful which has been done by someone, our first--not perhaps our best, but our first--instinct is to say, "Somebody's got to pay for this." Justice seems to demand that someone take some concrete action to set the moral scales in balance again.
The bad things that human beings do are likewise events in the moral order of things. To put the matter somewhat inelegantly, we do savage, immoral, despicable things to each other every day, with barely a casual acknowledgment of our culpability. We frankly, deserve punishment. This view of our just deserts is not very popular these days. But consider what life would be like if we did not accept the awfulness of our actions. We would be saying that the atrocious things we do are not important. And, to posit the existence of a God who is willing to brush off human failure and perversity would be to create a God who is indifferent to moral good and evil. "Somebody has got to pay for this" is a statement which can be self-serving and distracting. But it can also be a clear statement about the degree to which human sin has tipped the balance of the moral order.
The suffering of Jesus restores the balance. By living a sinless life, Jesus sets himself against the powers of his day, just as the virtuous still, today, inspire the hatred of the malevolent. And his steadfast righteousness attracts the animosity of sinful men and women and causes him to suffer. His suffering restores the moral balance as he absorbs into his body, into his being, the consequences of our alienation from God and from each other. So, the suffering of Jesus is an event in the moral order.
The suffering of Jesus is an event which measures love. Years ago, I happened to become slightly acquainted with Catherine Hearst at the time that her daughter, Patricia, was kidnapped by and later became a part of a violent left-wing paramilitary group. I remember seeing Mrs. Hearst after church one day and looking into her eyes. Whatever one might think of the Hearst family, or of Patricia or her political dalliances, in the eyes of that woman was the pain of love that I suspect only a mother can feel. The cost of love is often very high indeed. As I looked at that San Francisco society matron that day, I did not see a mover or a shaker in popular culture or an heiress to a newspaper fortune. I saw a tired, middle -aged woman aching with sorrow for her daughter in pain.
The suffering of Jesus shows us what it is like when God decides to love the whole human race on its own terms and in its own form. It is a costly undertaking, and the suffering is calculated on the cross.
The suffering of Jesus is also a proclamation of redemption. That is fancy theological language for a simple and remarkable truth: That the suffering of Jesus shows us those aspects of broken human life which God is setting out to fix. In order to understand redemption, one needs to remember that in Christianity the suffering of Jesus is never, ever properly considered without connecting it to his resurrection. Each of the wounds of Jesus are healed in the resurrection. Jesus rising to new life is a precise, item-by-item statement by God that suffering is not to be the last word.
Having a suffering God means having a relevant God. Jesus suffered because it is the lot of human beings to suffer. The suffering of Jesus is a statement about the solidarity of God with the human race. God did not sit in some heavenly precinct somewhere and behold the sickness, dishonesty, adultery, and tragedy of human life and say the cosmic equivalent of "Gee, that's too bad." Rather, God, in Jesus Christ got involved and lived just exactly the kind of life we must live. The important thing about the passion of Christ is that it shows Jesus enduring all the suffering we must endure. The whole ugly human scene appears in the passion: Political corruption and betrayal, abandonment by friends, harsh words carefully honed to hurt, hypocritical religious leaders who make us squirm, crass manipulation for financial gain, the loss of someone you thought loved you dearly--everything that is wrong with human life is displayed and worked out on Calvary.
The suffering of Jesus is outlined in such graphic detail in the gospels, because the "gospel"--the good news--is that God intends to do something about each and every aspect of human suffering. It is all in there because God intends to do something about all of it. Christ's suffering shows God's willingness to share in even the most painful details of the human situation. Christ's suffering is an essential event in the moral order, which shows the depth of God's love for us, a love that reaches across the full extent of our own suffering which God wants to fix.