I think there are two things about living in a godless universe that scare some people. First, there is no one watching over them, benevolently guiding their lives. Second, because there is no life after death, it all feels rather bleak.
Instead of scaring me, I find these two things incredibly liberating. It means that I am free to do as I want; my choices are truly mine. Furthermore, I feel determined to make the most of the years I have left on this planet, and not squander it. The life I live now is not a dress rehearsal for something greater afterwards; it empowers me to focus on the here and now. That is how I find meaning and purpose in what might seem a meaningless and purposeless existence; by concentrating on what I can do, and the differences I can make in the lives of those around me, in the short time that we have.