Yesod, is the ninth sephira of the Tree of Life spoken of in the Kabbalah, it is the symbol of pure life. Very often, synonymous with deprivation and restraint that lead to oppression and thinness or even perversion, purity has been an early death of the individual. What Master Omraam Mikhael Aivanhov shows us, taking a stand against this partial and erroneous perception of purity, presents it, on the contrary, as a world of extremely rich and creative life, still unknown and unexplored, founded on an accurate knowledge of psychic and spiritual life. Taking purity as the basis of his spiritual Teaching, (Yesod in Hebrew means "base", "foundation"), Master Omraam Mikhael Aivanhov rediscovers the meaning of the applications of ancient Initiations which he enriches with many discoveries he himself made. The rules and exercises he gives and which he experimented with for a long time himself, liberate man and awaken within his entire being the bubbling and harmonious forces of divine life. In this book on the Mysteries of Yesod, Master Omraam Mikhael Aivanhov makes us feel how much the life of a spiritual Master is like this "river of life" that purifies in its passage all those who approach it.