The Book of Mormon. This identification is based on a misinterpretation of Ezekiel 37:15-19. Mormons identify the stick of Ephraim with the Book of Mormon because it supposedly is the history of Ephraim in the new world (see D&C 27:5). The Ezekiel passage, and the LDS interpretation of it, is one of the first things Mormons learn.
Dictionary of Mormonese
Stick of Ephraim
Dictionary of "Mormonese"
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