The universe indeed, has not prescribed in its laws, a purpose for human beings, or a set of morals to uphold. The only purpose evolution gives us is to pass on genes. Hardly inspiring. I think instead, that we should spread our beliefs. How should we treat people? What is moral, what's not? Let's move humanity ever so slightly and slowly closer to our ideals.
Its true that we all only have a tiny part to play, and that really goes for all of us. Society is huge, and it changes slowly. People act on their beliefs, and anyone could change a few people, contributing to the slow shift of rhetoric and societal values and beliefs.
Another somewhat unrelated thing that might help you is the disbelief in Free Will - for that, check out Sam Harris' seminar on it: https://youtu.be/pCofmZlC72g