Why the human world is full of Suffering?

Well, as a believer of God, I can only say that this could maybe be like a test. If you p it, it's good for you and even others (i.e. When you see someone smile, it just makes you want to smile too, even if you're down in the dumps). But if you fail it, that would affect you and possibly others. I believe that at one point one point of time, everyone will have understood the meaning of life beyond what it is simply. And then at that time, everything will be 'nothing.' Time stops, happiness and sadness stops, and even life and death will stop. But then we won't feel sad everything will be gone, as we will understand why/how things happened the way it did, and accept it as God's choice. But note; this is spiritually speaking. In a more scientific way, everything will end (maybe slowly) when the sun dies out or some gigantic natural disaster wipes out most kinds of living things. So, this may not answer your question, but this is my point of view of how things might work out.