Although Sufism is the essence of all religions and its influence is upon all, yet it can more justly be called the esoteric side of Zoroastrianism, Judaism, Christianity, and Islam. But it is not a purely Zoroastrian esotericism devoid of Jewish influence, nor is it a solely Jewish mysticism free from the influence of Christianity, nor is it entirely Christian wisdom untouched by the morals of Islam. Therefore it is justifiable to call it the true spirit of all religions, even of those as foreign to it as Vedanta and Buddhism.