This is a historical document which defends the authenticity of the controversial Book of Abraham, part of the canonical Pearl of Great Price. The Book of Abraham was purportedly translated from an Egyptian manuscript purchased by the Mormons from a travelling show in 1835, long before their trek to Utah. Joseph Smith quickly produced a translation of this document, claiming it was written by Abraham in his own hand. Since modern knowledge of the Egyptian writing system was in its infancy at this time, there was no way to verify this claim.
The manuscript disappeared for many years until it resurfaced in 1967 in the Metropolitan Museum of Art in New York. At that time Egyptian experts verified that it was actually a papyrus of a portion of the Book of the Dead.
Notwithstanding, the Book of Abraham is still considered part of the Pearl of Great Price and is held to be authentic by devout Mormons. This does not invalidate Mormon doctrine; any sacred text which has have signficance for the faithful should be considered valid on its own terms.
Keep in mind that this is actually a very typical story of the origin of many sacred texts, including all of the best known ones; the difference is simply that it played itself out recently instead of in the misty past. --J.B. Hare.