The issue of sickness is always a difficult one to deal with. The key to remember is found in Isaiah 55:9 (NKJV); For as the heavens are higher than the earth, So are My ways higher than your ways, And My thoughts than your thoughts.
When we are suffering from a sickness, disease, or injury, we usually focus solely on our own suffering. In the midst of a trial of sickness, it is very difficult to focus on what good God might bring about as a result.
Romans 8:28 (NKJV)
And we know that all things work together for good to those who love God, to those who are the called according to His purpose.
Many people look back on times of sickness as times when they grew closer to God, learned to trust Him more, and/or learned how to truly value life. This is God's perspective because He is sovereign and knows the end result.
This does not mean sickness is always from God or that God always inflicts us with sickness to teach us a spiritual lesson. In a world tainted by sin, sickness, disease, and death will always be with us. We are fallen beings, with physical bodies prone to disease and illness. Some sickness is simply a result of the natural course of things in this world. Sickness can also be the result of a demonic attack.
In Matthew 17:14-18 and Luke 13:10-16, the bible describes several instances when physical suffering was caused by Satan and his demons. So, some sickness is not from God, but from Satan. Even in these instances, God is still in control. God sometimes allows Satan to cause physical suffering. Even when sickness is not directly from God, He will still use it according to His perfect will. Sickness and suffering are never easy to deal with. One thing is for sure, sickness should not cause us to lose faith in God. God is good, even when we are suffering. Even the ultimate of suffering—death—is an act of God’s goodness. It is hard to imagine that anyone who is in heaven as a result of sickness or suffering regrets what they went through in this life. One final note; when people are suffering, it is our responsibility to minister to them, care for them, pray for them, and comfort them. When a person is suffering, it is not always appropriate to emphasize that God will bring good out of the suffering. Yes, that is the truth. However, in the midst of suffering, it is not always the best time to share that truth. Suffering people need our love and encouragement, not necessarily a reminder of sound biblical theology. “And we know that for those who love God, all things work together for good, for those who are called according to his purpose.”