 Such was the doctrine of metempsychosis or the transmigration of souls, as a justification of the ways of God to man, prevailing among the Hindus of all classes and sects, the Pythagoreans, the Orphic mystics and the Druids among the Celts.The doctrine of a forensic judgment in the unseen world, by which the eternal lot of departed souls is determined, was also widely prevalent in pre-Christian times.The Pharaonic Egyptian idea of the judgment is set forth with great precision of detail in the "Book of the Dead", a collection of formulas designed to aid the dead in their passage through the underworld.