I think the explanation for why Jesus had to suffer is that Jesus served in a role similar to Job in that he proved it is possible for a human to remain faithful to God even under great trial and suffering. So they say that Jesus' faithful endurance of suffering proved false Satan's charge that humans only serve God in favorable circumstance and abandon him when things get bad. But there's another side to the subject of human integrity that neither Job or Jesus answered and that has never be tested and it's this:
Do humans serve God because they truly love him, or because of the promise of a future reward for the faithful and destruction for the unfaithful?
This is the more important test of integrity that the bible does not address. As long as there is a reward for obedience and punishment for disobedience, it cannot be demonstrated that human's obedience to God is borne of pure love untainted by selfish motives.