The world of today is a product of a long history of disobedience to God and His teachings.  We see from Adam and Eve to the early Israelites that humankind wanted to make their own decisions.  The only healing from the physical and mental sickness though will come from God's Plan.  We can be healed now spiritually through repentance and we can be a part of healing all nations when Jesus Christ returns to this earth to restore and refresh all things.