The Realms Beyond is a tome found on the 4th level of the labyrinth in the original Diablo. Archbishop Lazarus is presumed to be the writer, and the text is about how he came to know of the meaning of the Sin War by Diablo.

It reads as follows:

"All praises to Diablo - Lord of Terror and Survivor of the Dark Exile. When he awakened from his long slumber, my Lord and Master spoke to me of secrets that few mortals know. He told me the Kingdoms of the High Heavens and the Pits of the Burning Hells engage in an eternal war. He revealed the powers that have brought this discord to the realms of Man. My Lord and Master has named the battle for this world and all who exist here the Sin War."
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