Paul Tautges has posted Joni Eareckson Tada’s list (from When God Weeps: Why Our Sufferings Matter to the Almighty) of God’s purposes in our suffering. You should read the whole list, but there are three central ones especially worthy of note.
These first two might sound simple, but they strike at the core of a major misunderstanding of Christianity in our culture today. Whenever I’m asked a question about suffering, I find myself having to begin here:
If only I could convince every Christian in our culture of those two things! There is an assumption behind many Christians’ confusion about suffering that God’s main purpose is for us to be happy (i.e., free from pain). But joy in God is not the same as comfort, and neither is maturity. We’ve set our expectations on something false, and when God fails to deliver, we lose trust in Him. It’s better we learn those two purposes before we begin to suffer.
The third purpose is the most important:
Suffering is used to increase our awareness of the sustaining power of God to whom we owe our sustenance (Ps 68:19).
And it doesn’t just increase our awareness, it increases our dependence. If I had to choose the most important lesson I’ve learned from suffering, this would be it. There is nothing like suffering to humble you before God, to reveal your true position as powerless creature beneath the Creator, to highlight your distressing weaknesses and lack of trust in Him.
When you finally find yourself identifying with the sick and desperate crowd in the Gospels, with eyes lowered, hoping only to touch the hem of His garment, when you wake up in the morning and drop immediately to your knees out of sheer need, that's when you know suffering has done its job.
When He uses you now, there will be no mistake about Who gets the glory.