Sufism has understood what is behind the ideal of Ahura Mazda and Ahriman, the good principle and the evil principle. One finds this in the words of Christ and in the Quran as well as in the Zend Avesta. It has understood what is behind the idea of angels. And it has idealized God and the Master, the deliverer of the divine message. It may be called Jewish mysticism, without omitting the influence of Christianity. It may be called the wisdom of the Christians, without omitting the wisdom of Islam which is to be found in it. It may be called the esoteric side of Islam, without neglecting the influence of philosophies as foreign as those of the Vedanta and Buddhism. This is the reason why it is so wide, perfect, and universal.