Rexaura

In both Path of Radiance and Radiant Dawn, Rexaura is the most powerful Light Magic tome.

To obtain it in Path of Radiance, you need to follow these steps:


 * Wound the Bishop holding it to at most half HP remaining (if it doesn't work, try weakening it further without killing him)
 * Wait another turn for him to chug himself an Elixir off

By then, he should have de-equipped his Rexaura, you can then steal it.