Originally the Philosopher’s Stone was believed to be the chemical that changed base metals into silver or gold, often it was termed the Power of Projection.
It was first mentioned by Zosimos the Theban (c. 250-300) in the third century. Throughout the generations the Philosopher’s Stone has taken on an immense range of powers; not only has it been called the secret of life and health, but also possessing spiritual significance.
The notion of its spiritual qualities expanded until in the thirteenth century a program evolved that led the alchemist through a strict devotional ritual and purification. After completing this ceremony he was thought worthy to perform his activities.
Eventually the Philosopher’s Stone was thought to signify the force behind the evolution of life and the universal binding power which unites minds and souls in a human oneness.
Finally, it represented the purity and sanctity of the highest realm of pure thought and altruistic existence. A.G.H.
Source: 2.