Why do human beings exist?

To start, I am not asking HOW we exist, how we came to be or to discuss religion. I do believe that God made us and the entire universe, but I see it as more broad than that. Just as we are all made of matter and tiny particles that work together to form a whole system, have you ever thought that we are part of a whole that we know nothing about? Maybe we are the cells, or even the parasite that spreads. What I want to know is what theories other people may have. What do you think?