"Be careful, God is watching." A warning to keep your behavior within moral boundaries... IF you believe in God.
But if you don't, or at least have doubts, you have to look somewhere else for hour moral underpinnings. And that's been an argument for much of history: whether you can be sufficiently moral without religion.
Of course, says sociologist Phil Zuckerman. He teaches and writes about secular vs religious morality. And we had a chance to hear his thoughts on the subject, in this interview from 2017.