Everything in this Universe of differentiated matter has its two aspects - the light and the dark side - which two attributes applied practically, lead, the one to use, the other to abuse. Every man may become a botanist without apparent danger to his fellow-creatures; and many a chemist who has mastered the science of essences knows that each can both heal and kill. Not an ingredient, not a poison, but can be used to do both - eye, from harmless wax to deadly prussic acid, from the saliva of the infant to that of the cobra de capella. This every tyro in medicine knows - theoretically, at any rate. But where is that learned chemist in our day who has been permitted to discover the "night side" of an attribute of any substance that enters into the three kingdoms of Science, let alone the seven of the Occultists, i.e., who of them has penetrated into its Arcana, into the innermost Essence of things and its primary correlations? Yet it is this knowledge alone which makes of an Occultist a genuine practical Initiate, whether he turns out a Brother of Light or a Brother of Darkness. The essence of that subtle, traceless poison, the most potent in nature, which entered into the composition of the so-called Medici and Borgia poisons, if used with discrimination by one well versed in the septenary degrees of its potentiality on each of the planes accessible to man on earth, could heal or kill every man in the world; the result depending, of course, on whether the operator was a Brother of the Light or a Brother of the Shadow. The former is prevented from doing the good he might, by racial, national, and individual Karma; the second is impeded in his fiendish work by the joint efforts of the human "Stones" of the "Guardian Wall
Helena P Blavatsky