One of the most beautiful pictures of God working through human illness and even using that illness to bring about His perfect work through His followers is in the story of Amy Carmichael.
Amy felt called to go into mission work in her teen years, and her heart was set on going to Japan. When she finally got to Japan, it became apparent that she couldn't stay. The climate agrivated some serious health problems and the mission organization forced her to go to India instead. Amy didn't plan to go to India - she had felt that Japan was her mission-field. But through a tender heart to God Amy began working in India to spread His love to this country. Amy was horrified by the common practice of selling children into temple prostitution, and eventually started a home called Donover where she would work to rescue these child slaves and give them a home. This home is still in existence today even though Amy died in the 1950s. The home for children is now run by former child slaves that were rescued by the ministry Amy began. Amy has literally saved hundreds of children in India from this dreadful trade of selling children into temple prostitution; but she never would have been in India if she had not become so ill while in Japan. God used her illness to get her right where He wanted her. (read the story of Amy in Elizabeth Elliot's book: "Chance to Die: The life and Legacy of Amy Carmichael")
In Galations 4:13 the Apostle Paul reminded the churches in Galatia that it was: "because of a bodily illness" that he had first preached the gospel to the Galatians. Paul clearly saw that sometimes God uses or allows physicall illness to lead us where He wants us to go. I have mentioned this passage and this concept before - but it bears repeating.
May I be willing and have enough faith to see that God can use my pain and illness to send me exactly where He wants me to be.