Most human suffering (outside of the inevitable decay of our bodies) comes from the acts of other humans. Putting people down, making them feel low, bragging, saying untrue things about others, cheating on others' wives, violently hurting others, refusing to help others when their luck is down, etc. etc. - all this comes from men's hearts. Though I certainly cannot speak for God(!), most religious people presume that God tolerates our suffering at the hands of others in order to give us a chance (of our own free will) to choose the right side in the great battle between good and evil on this earth. This was the example of Christ. He suffered immensely to show us how to stay true to the good (and the Godly), while accepting the suffering inevitably caused by evil in this world.