I'd highly recommend reading C.S. Lewis The Problem of Pain and thereafter A Grief Observed. They raise a lot of theological questions about the goodness of God, and why we're made to suffer. In the best way I can, I'd summarize by saying it's a test, or preparation rather for the glory of Heaven, much in the way Christ died on the cross for our sins. Without pain, God's love for us would have no meaning. There's a great deal more to it of course, but I've always considered his writings to be wonderful sources of guidance and reassurance, not to mention they're just enjoyable to read.