It's worth noting that the quoted fragment occurs in a book on Stoicism, which doesn't have a concept of personal god throwing you into hell, and it's a part of the explanation of a Stoic technique. In fact, I think the OP cut away a little too much context from the quote:

The Stoics are not alone in harnessing the power of negative visualization. Consider, for example, those individuals who say grace before a meal. Some presumably say it because they are simply in the habit of doing so. Others might say it because they fear that God will punish them if they don’t. But understood properly, saying grace—and for that matter, offering any prayer of thanks—is a form of negative visualization. Before eating a meal, those saying grace pause for a moment to reflect on the fact that this food might not have been available to them, in which case they would have gone hungry. [...]