S.a. Kapadia 
The Teachings of Zoroaster [EPUB ebook] 

“I WILL now tell you who are assembled here the wise sayings of Mazda, the praises of Ahura, and the hymns of the Good Spirit, the sublime truth which I see rising out of these flames. You shall therefore hearken to the Soul of Nature. Contemplate the beams of fire with a most pious mind! Every one, both men and women, ought to-day to choose his creed. Ye offspring of renowned ancestors, awake to agree with us.” So preached Zoroaster, the prophet of the Parsis, in one of his earliest sermons nearly 3, 500 years ago.
Imbued from his infancy with deep philosophical and religious thoughts for the welfare and well-being of mankind, this ancient prophet of Bactria derived his holy inspiration after thirty years of divine meditation on a secluded and inaccessible mountain-top of “Ushidarena.” Thus fortified in communion with Ahura-Mazda, “Spitama Zarathustra” proceeded to the city of Balkh, at the time the capital of the King of Iran, Kava Vishtaçpa.
Clothed in pure white flowing vestments, bearing with him the sacred fire, “Adar Burzin Mehr, ” and a staff or sceptre made of a cypress tree, this sage of antiquity appeared before the court of Kava Vishtaçpa. By persuasion and argument he unfolded his religious mission; and proclaimed the mandate of Ahura, in order to elevate the ancient faith of the Aryas to its lofty and intellectual purity of monotheism.