“It is but natural that we should see in the appellation of Zoroaster not a name but a generic term, whose significance must be left to philologists to agree upon. Guru, in Sanscrit is a spiritual teacher; and as Zuruastara means in the same language he who worships the sun, why is it impossible, that by some natural change of language, due to the great number of different nations which were converted to the sun-worship, the word guru-astara, the spiritual teacher of sun-worship, so closely resembling the name of the founder of this religion, became gradually transformed in its primal form of Zuryastara or Zoroaster?
The opinion of the kabalists is that there was but one Zarathustra and many guruastars or spiritual teachers, and that one such guru, or rather huru-aster, as he is called in the old manuscripts, was the instructor of Pythagoras. To philology and our readers, we leave the explanation for what it is worth. Personally, we believe in it, as we credit on this subject kabalistic tradition far more than the explanation of scientists, no two of whom have been able to agree up to the present year.
Aristotle states that Zoroaster lived 6,000 years before Christ; Hermippus of Alexandria, who is said to have read the genuine books of the Zoroastrians, although Alexander the Great is accused of having destroyed them, shows Zoroaster as the pupil of Azonak, (Azon-ach, or the Azon-God), and as having lived 5,000 years before the fall of Troy. Er or Eros, whose vision is related by Plato in the Republic, is declared by Clement to have been Zordusth. While the Magus who dethroned Cambyses was a Mede, and Darius proclaims that he put down the Magian rites to establish those of Ormazd, Xanthus of Lydia declares Zoroaster to have been the chief of the Magi!
Which of them is wrong? Or are they all right, and only the modern interpreters fail to explain the difference between the Reformer and his apostles and followers? This blundering of our commentators reminds us of that of Suetonius, who mistook the Christians for one Christos, or Crestos, as he spells it, and assured his readers that Claudius banished him for the disturbance he made among the Jews.”
H. P. Blavatsky
The Mark Of God: Understanding Your "I AM Presence" 