A time traveler, Roy, is marooned in the ancient era. Time and place are negotiable: ancient Greece, Roman Judea, ancient China, etc. There's no hope of getting back, but he's an intelligent fellow with a good background in basic science. Roy has made a good living for himself by setting up a distillery, but he decides to make a bigger impact. He starts a new religion, Royism, but with the intent that the rituals and tenents are of practical benefit to believers.
For example, the holy text contains the following: "Before readying water for drinking, your ROY commands that you bring it to a boil and recite the litany of belief." And the litany of belief just happens to take around three minutes to recite.
His goal was to encode as much modern, practical knowledge into his religion as possible so that humans could benefit from the knowledge even if they didn't necessarily understand it. Roy is familiar with the way religions can mutate over time, he knows a Royble (that's a Royist Bible) can't just have diagrams of spinning wheels or seed drills in it. He formulates it to be pretty concise and resistant to being corrupted in translation.
Now fast forward a thousand years. Royism has spread widely, in large part, thanks to the observable benefits, but human foibles are ever-present. Over the years misinterpretation, heresies, and schisms have multiplied. For example, ultimately there are religious wars fought over whether the ROY intends for the water to come to a rolling boil or a simmer. But just one example doesn't make for an interesting world, and besides elementary hygiene, I'm drawing a blank on what Roy might have included and therefore what was misinterpreted and misconstrued over time.
In short, besides hygiene practices, what basic ideas from the present that can be summed up in a paragraph of plain language would have been of concrete benefit in the past?