Yes. After all these years, all these questions, I can say for sure that yes, God does have purpose--even in sufferings and disease and sickness (and in health).
When God shut me down and took away the things that defined my identity, my sense of significance, the pieces of action and activity that gave me a feeling of personal value, I felt the loss of them. Then, God filled those spaces up with His own dreams and goals for me. At first they felt less. I felt less.
Now as time passes and I see His purpose more clearly, I can even give thanks for my condition.
I have learned that God can do more with my "less" than I ever could have done with my more.
I suppose it's like the little boy who gave his five loaves and two fish to Jesus. Jesus fed 5,000 people with that meager little lunch. Had the little boy scraped and worked to earn the money to have bought and given ten loaves and 4 fish, would it have made any difference? Even if he could have tripled or quadrupled his own lunch, it was still ridiculously insufficient for the need.
The point wasn't how much the little boy could give. It was the fact that he gave what he had.
So with me, it is not meant to be about how much I can do for God, or what I can accomplish. Rather, God wants me to offer who I am, even this less that I am, and watch Him do a miracle with it.
In my health, I was trying to feed the 5,000 with my own limited supply, my own strength. How silly. Now, I can live knowing my weakness is His strength.
You can too. If you have a chronic condition, God has a purpose for it. He has a purpose for you in it. He can do more through your weakness than you could have in your strength. Keep faith. Keep hope. A smaller lunch is no limitation when Jesus gets a hold of it!