To the people that try to argue that there is no good or bad. To the people that think is all a matter of opinion. It is really black and white. Not so much gray. If you murder someone because you don't like the way they talk its bad. If you help someone that you don't know and never ask for recognition than that act is good. If you steel someones car because you like it better than the peace of crap you drive, its bad. You see how this works. We all know these things to be facts of life. But for some reason people try to use this post modern crap to give them a reason to do what they know is bad. Its all crap.
But as for the original question. The purpose of life is to glorify and to have a relationship with God. To be fruitful and multiply, to have dominion over the earth. To experience Joy. Unfortunately in order to have joy we must also know pain. To know Jesus will bring joy to your life and that will be good.