At present we have to consider, not what the exact tenets of the Zoroastrians were, but only the mode in which Artaxerxes imposed them upon his subjects.
The next step, after settling the true text of the sacred volume, was to agree upon its interpretation.

The language of the Avesta, though pure Persian, was of so archaic a type that none but the most learned of the Magi understood it; to the common people, even to the ordinary priest, it was a dead letter.

Artaxerxes seems to have recognized the necessity of accompanying the Zend text with a translation and a commentary in the language of his own time, the Pehlevi or Huzvaresh.

Such a translation and commentary exist; and though in part belonging to later Sassanian times, they reach back probably in their earlier portions to the era of Artaxerxes, who may fairly be credited with the desire to make the sacred book "understanded of the people." Further, it was necessary, in order to secure permanent uniformity of belief, to give to the Magian priesthood, the keepers and interpreters of the sacred book, very extensive powers.

The Magian hierarchy was therefore associated with the monarch in the government and administration of the State.