<s>The only classes that can create spellbooks are arcane, and they can only learn arcane spells, so they cannot create a divine spellbook. As a result, there is no such thing as a divine spellbook, and officially, a divine spellcaster with *mnemonic vestment* is stuck using scrolls. This isn’t a huge hardship, but it is one.</s> Turned out to be incorrect, see [pi4t’s answer](https://rpg.stackexchange.com/a/157922/4563).

Personally, I let divine spellcasters produce “prayerbooks” for this purpose if they like. I made the same ruling for [a warpriest with the arcane bond ability](https://rpg.stackexchange.com/a/154719/4563), for example. And I also use D&D 3.5e content, which includes the archivist class from *Heroes of Horror*—which explicitly and officially [keeps a prayerbook, being a kind of divine wizard](https://rpg.stackexchange.com/a/35140/4563). But the official rules wouldn’t let you do that. And it’s hard to argue with someone who wants to limit the effectiveness of *mnemonic vestment*, seeing as it is **extremely** powerful.