I would agree with Pasteur that a disease mostly occurs when the organism is too weak to defend itself - we are under constant attack from diseases, but at one time, due to one reason or another, we become too weak to defend, and therefore we have a disease. I would qualify diseases, suffering and misfortune as a challenge to improve ourselves or our wrong attitudes. Tolkien wrote several times, in both Akallabeth and Athrabeth Finrod ah Andreth, that is it the wrong attitudes of Men that lead to their shortening of lives. I believe that the reverse is also true. This brings our discussion to a very interesting level: is there anything outside Eru, which is not permeated by Him?