Somebody, who lives among us, would perhaps bring evil, bad qualities to light if he followed his lower nature, but within him, mixed with the lower nature, the higher one lives which keeps it in check. You can compare this mixture with a mixture of a yellow liquid and a blue one in a glass, resulting in a green liquid in which we can no longer distinguish yellow and blue. The lower nature is mixed with the higher one in the human being that way and both are not to be distinguished. As you can extract the blue liquid from the green liquid by chemical means, so that only the yellow fluid remains, and the uniform green is separated into a duality, in blue and yellow, you separate the lower nature from the higher one by means of the esoteric development. You pull the lower nature out of the body like the sword from the scabbard, which remains alone then for itself. This lower nature comes out in such a way that it appears almost nightmarish.
When it was still mixed with the higher nature, nothing of it was to be noticed. Now, however, when it is separated, all evil, bad qualities come out. Human beings who had seemed benevolent before often become quarrelsome and envious. These qualities sat already in their lower nature, however, were controlled by the higher one. You can observe this with many people who are led on anomalous ways. The human being becomes a liar very easily when he enters the supersensible world. He easily loses the ability to distinguish true from wrong. It belongs inevitably to the esoteric training that the strictest training of the character is paralleled by it. What history tells of the saints as their temptations is not a legend but literal truth.
Source: Rudolf Steiner – GA 54 – The Riddles of the World and Anthroposophy: Inner Development – Berlin, 7th December 1905