God teaches us a little at a time. He doesn’t want us to be overwhelmed by sorrow. Why sorrow? When God shines His light on our heart and we actually see what is in there, we are sorrowful. It’s a sorrow unto repentance. The pain we have because of sin, ours and the world’s, motivates us the action. When we are motivated to share the gospel, the world will react. They will fight back. We will be persecuted. Some of us will die. Jesus explained it in John 16. But Jesus said because I go to my Father, I will send the Comforter, the Spirit of God. He will lead us an guide us into all truth. Then we will see as God sees. This is the sorrow that the world will rejoice in.