Osiris is the father of the god Horus, Osiris as having been killed by his brother, Set, who wanted Osiris' throne. His wife, Isis finds the body of Osiris and hides it in the reeds where it is found and dismembered by Set. Isis retrieves and joins the fragmented pieces of Osiris, then briefly brings Osiris back to life by use of magic. This spell gives her time to become pregnant by Osiris before he again dies. Isis later gives birth to Horus. As such, since Horus was born after Osiris' resurrection, Horus became thought of as a representation of new beginnings and the vanquisher of the usurper Set.
It should be remembered that Walis Budge considered himself a priest of Osiris and not just an archaeologist and academic! Ithil Colquin in her book "The Sword of Wisdom" a biography of McGregor Mathers has provided evidence that Budge was an Adeptus Minor of the Golden Dawn and that he ran a temple in the British Museum. The Adeptus Minor degree involved a symbolic ritual in which the candidate dressed in Ancient Egyptian regalia lay down in a sarcophagus in the position of Osiris and was subsequently "resurrected" as a priest of Osiris, leaving behind an "empty Tomb" just as in the Great Pyramid.
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