This is the same feeling that's been translated in such similar ways into every major religion
in existence. For the monotheists, it give credence to the fact that the wicked gluttons are going to be punished later on, while for the eastern religions it teaches that self-sacrifice is the key to
true enlightenment and happiness. It is why rich chocolate is sometimes described as "sinful" and why Buddhist monks elect to own
nothing save for a saffron robe and begging bowl. It is also the main reason the so many of the catholic deadly sins are indulgent in nature and why most of the several virtues urge temperance. If you think about it, the virtue of asceticism has been incorporated into almost every code of morality ever created. The main exception is hedonism which I'll come back to.
It is interesting to note that Satanism is actually less of a worship of the devil as perceived by the christian church and more of a rejection of the christian god accompanied by a plethora of indulgences: food, alcohol, mass orgies, occasional violence, etc. This is why atheists are sometimes referred to as satanists only with less indulgence and why radical muslims regard America, land of the gluttonous, as "the Great Satan".
The instinct originated in man's hunter-gatherer past which we are not at all yet separated from. Dawkins argued in "The Selfish Gene" how a number of moral values could have evolutionary origins (blog post on this topic to come) and it makes sense that the basis for so much of our ethics would have similar origins.
Imagine a tribe of wandering homo sapiens. Being a few generations' worth of descendants from a common family member, they are all fairly closely related. One of the hunters in the tribe kills an animal for food. Do his genes have a better chance of being passed along if he consumes the entire animal himself, or if he shares the spoils with the rest of the tribe? Obviously the answer is the latter, but if you'd like a better explanation of the scenario, I suggest reading the first few chapters of Dawkins' "The Selfish Gene".
The gist of the argument is that we are instinctually programmed to want to pass along our genes to another generation, and seeing as that we're all at most 40th cousins, we stand to gain at least a little for every selfless act we perform.
So what should you do with this information? Wheatever you want; it's a perk of being a rational person, remember? Just keep this in mind the next time someone tells you that it's impossible to be good without god.