That’s a very good question you pose (aside from your implication that religion is a superstition). I had to think about it for a while, because I find superstitions rather foolish (though sometimes in an endearing, sometimes in an annoying, and sometimes in a dangerous way), while I can respect religious beliefs (some of them at least), even ones I do not personally share. But when I try to define the difference, it gets a little tricky.
For one thing, “superstition” usually refers to a specific belief or practice, while a “religion” is a whole integrated system of beliefs, practices, traditions, ethical rules, cultural norms, communities, hierachies, etc.
But the question is really, what’s the difference between a superstitious belief and a religious belief? Well, after thinking it over for an hour or two, here’s what I came up with:
In the words of Stevie Wonder, “When you believe in things that you don’t understand,” that’s superstition. That is, a superstitious belief reflects a lack of understanding, specifically of cause and effect. If you believe that X causes Y, without any notion of how or why, that’s a superstition.
For example, if you claim that riding a motorcycle without a helmet brings “bad luck” or misfortune, this is not a superstition if you have a pretty good idea how it can lead to misfortune. If you claim that breaking a mirror brings bad luck, or that carrying a rabbit’s foot brings good luck, without giving any good reason how or why this could work, that’s a superstition. If you claim that that there is a God (or one of the gods) who decides to punish mirror-breaking by inflicting misery on anyone who does it, I would not call this a superstition but a religious belief (probably a wrong or silly religious belief, at least unless you could show me some bigger picture within which such a belief makes sense, and/or provide statistical evidence of a correlation between mirror breaking and misfortune; but still, a religious belief as opposed to a superstition).
Astrology, for example, I consider a superstition rather than a religious belief, because I have yet to hear a reasonable explanation for how the position of the stars on the date of ones birth could influence ones personality or lot in life.
It’s true that some people have superstitious beliefs mixed in with their religion, or hold religious beliefs for superstitious reasons. It’s also true that some people have superstitious beliefs mixed in with their science, or hold scientific beliefs for superstitious reasons. One person might kneel when he prays because he thinks that his prayers “work” better that way or God hears him better when he’s on his knees (without really thinking about why he thinks so): superstition. Another person might kneel when he prays because it helps him concentrate and get in a prayerful frame of mind, or it’s his way of humbling himself before God: not superstition.