" For this reason the ancients often compared the symbol to water, a case in point being tao, where yang and yin are united. Tao is the “valley spirit,” the winding course of a river. The symbolum of the Church is the aqua doctrinae, corresponding to the wonder-working “divine” water of alchemy, whose double aspect is represented by Mercurius. The healing and renewing properties of this symbolical water—whether it be tao, the baptismal water, or the elixir—point to the therapeutic character of the mythological background from which this idea comes. Physicians who were versed in alchemy had long recognized that their arcanum healed, or was supposed to heal, not only the diseases of the body but also those of the mind. Similarly, modern psychotherapy knows that, though there are many interim solutions, there is, at the bottom of every neurosis, a moral problem of opposites that cannot be solved rationally, and can be answered only by a supraordinate third, by a symbol which expresses both sides. This was the “veritas” (Dorn) or “theoria” (Paracelsus) for which the old physicians and alchemists strove, and they could do so only by incorporating the Christian revelation into their world of ideas. They continued the work of the Gnostics (who were, most of them, not so much heretics as theologians) and the Church Fathers in a new era, instinctively recognizing that new wine should not be put into old bottles, and that, like a snake changing its skin, the old myth needs to be clothed anew in every renewed age if it is not to lose its therapeutic effect. "
― C.G. Jung , Aion (Collected Works 9ii)