> Not a love letter or a sermon or a story, but a receipt. This probably reflects their ubiquity rather than importance.

We humans are pretty good at remembering sermons and stories and we can recreate them from memory and pass them down to the next generations. We however suck at remembering numbers, that's why we invented writing so we could write the numbers down and rely on these records, instead of on bad human memory.

Well, we especially suck at remembering numbers when it’s something like ‘how much I owe Bob’ hah. At least for many people.

I expect this writing was a way to help reduce civil unrest/murder by reducing he said/she said arguments about goods, services, money, etc.