The theory of Transmigration, or Metempsychosis, as it has been called by many philosophers, originally meant the passing of a soul from one body after death into another; or, in other words, it meant that the soul after dwelling in one particular body for a certain length of time leaves it at the time of death, and in order to gain experience enters into some other body, either human, animal or angelic, which is ready to receive it. It may migrate from the human body to an angelic body and then come down on the human plane, or to the animal plane and be born again as an animal.
So the original meaning of transmigration or metempsychosis was the revolution of the soul from body to body whether animal, human, angelic or of the gods. The migrating substance being a fixed quantity, with fixed qualities, chooses its form according to its taste, desire and bent of character. This idea prevailed among the ancient Egyptians, according to whom the soul, after leaving the dead body, would travel from one body to another for thousands and thousands of years in order to gain experiences in each of the different stages of life.
Among the Greek philosophers we find that Pythagoras, Plato and their followers believed in this theory of Metempsychosis or Transmigration of souls. Pythagoras says: “After death the rational mind, having been freed from the chains of the body, assumes an ethereal vehicle and passes into the region of the dead where it remains till it is sent back to this world to inhabit some other body human or animal. After undergoing successive purgations, when it is sufficiently purified, it is received among the gods and returns to the eternal source from which it first proceeded.” Plato also believed in this theory. Of course we cannot tell exactly from whence Pythagoras and Plato got these ideas.
Some say that they learned these doctrines from Egypt; others believed that, either directly or indirectly, they learned the theory of transmigration from India. Plato describes in “Phaedrus,” in mythological language, why and how the souls take their birth upon this plane, either as human or animal. He says: “In the heaven Zeus, the Father and Lord of all creatures, drives his winged car, ordering all things and superintending them. A host of deities and spirits follow him, each fulfilling his own function. Whoever will and can follows them.
After taking this round, they advance by a steep course along the inner circumference of the heavenly vault and proceed to a banquet. The chariots of the gods, being well balanced and well driven, advance easily; others with difficulty; for the vicious horse, unless the charioteer has thoroughly broken him, weighs down the car by his proclivity towards the earth, whereupon the soul is put to the extremity of toil and effort. The souls of gods reach the summit, go outside and stand upon the surface of heaven, and enjoy celestial bliss. Such is the life of the gods; other souls which follow God best and are likest to Him succeed in seeing the vision of truth and in entering into the outer world with great difficulty.
The rest of the souls longing after the upper world all follow; but not being strong enough, they are carried round in the deep below, plunging, treading on one another, striving to be first, and there, in confusion and extremity of effort, many of them are lamed and have their wings broken. Thus when the soul is unable to follow and fails to behold the vision of Truth, sinks beneath the double load of forgetfulness and vice, her feathers fall from her and she drops to earth and is born again and again as human beings or as animals.”