In the world of Watership Down, the largest number in rabbit language is five, because rabbits can only count to four and thus anything more than that is “five.” The author doesn’t go into rabbit math in detail, but if we think about it, this is really a pretty simple mathematical system. The sum of anything more than 2+2 is five, the product of anything more than 2×2 is five, five minus anything is probably going to be five, and there is no division because rabbits can only multiply.
This strikes me as resembling certain modes of thinking. The whole appeal is its simplicity. Anyone can do it. Granted, there are some drawbacks: if all you know is rabbit math, most of real math will be incomprehensible to you. But rabbit math has a way of dealing with that incomprehensible complexity. It’s all just “five.” That’s all you can say, and in rabbit math that’s all you need to know. Much better than real math, which gets notoriously harder the farther you go. Even people who like math are going to have to do considerable work to master more than the basics. Rabbit math is easier.
You’re right, I’m thinking about religion. Granted, there are a lot of people who think religiously without going all the way to rabbit-math-level oversimplifications. But that’s the limit towards which religious thinking tends. Its appeal is that it simplifies things, and has a place to stick the incomprehensible. Magic (or miracles, if you prefer) covers everything beyond a certain level of understanding, and in religious thinking that’s all you need to know.