Those who belonged to the faith believed that they would be resurrected after death and judged on their lifelong deeds.
Zoroastrianism existed in Iran by the time Medes and Persians were established. They both treated it and received it as a long-established faith, with its doctrines and observances already defined and a canon of works in the Avestan tongue. There is no evidence that the literature was written down at this time and it was orally transferred from one generation to the next. The claim by the later Iranians that Alexander the Great destroyed the massive texts has not been substantiated."
When the Arabian invasion of the Persian empire was complete there were traditions developed designed toward the psychological attitudes that Muslim was the better or more correct faith. The taxes were paid with ritual and decorum. For instance the person doing the paying had to stand while the other person sat and was waited on. The person doing the paying had to hold the tax funds out with open palm for the receiver to accept it.
The dhimmi has to stand while paying tax and the officer (emir) who receives it sits. The dhimmi has to be made to feel that he is an inferior person when he pays. He offers the poll tax on his open palm. The emir takes it so that his hand in on top and the dhimmi's below. Then the emir gives him a blow on the neck, and one who stands before the emir drives him roughly away. The public is admitted to see this show."
Originally when the take over was complete most Iranians refused to convert to Islam. They stayed true to their faith and stood proud with their heads high as they practiced it. It was only after law upon law, tradition after tradition and mandate after mandate was heaped upon them that they began to covert. To make the process even more sure the Zoroastrians were made to feel like second class citizens. In addition, they were forced to conduct themselves and present them selves to the world as second class citizens when they went out anywhere or conducted business anywhere.
All these pressures, humiliation at the time of paying jizya, deliberate destruction of temples and forced conversions resulted in massive conversions. There are accounts of Muslim rulers forcing mass circumcision on the newly converted males to make sure they had truly become Muslims. The Arab governor of Sogdia was faced with 7000 males reconverting back to Zoroastrianism once circumcision was forced on them. Tabari records that Arab tax collectors in the eight-century would mistreat Zoroastrians, tearing off the sacred girdle and hanging it round their necks in derision."
Perhaps the most difficult blow for the Iranians to take was the forced change to Arabic of the books. This created the psychological understanding that the Arabs were there to stay and they were the dominant faith regardless of the Iranians determination to hang onto their religious past. (Schindler, 2004)
When the tribes of Arabia united under the banner of Islam in the seventh century, they were able to cut through the rotted shreds of the Byzantine and Persian empires to forge a new and dynamic power.
They saw their duty as bringing the true faith of Islam to the infidels surrounding them, and felt that military conquest was the best, the most rapid, and the surest way of doing this. If they managed to enrich themselves in the process, surely it was but a just reward for accomplishing what was divinely ordered. "
If one looks at first appearance it seems that the Zoroastrains were forced to convert to Muslim. The many changes that took place in their daily existence once the Arab invasion of Persia was over appears intitially to have forced the Zoroastrains to convert to Muslim.
The changes in the clothing they had to wear, the marriage constrictions, and the business restrictions all worked to provide a strong psychological push to convert.
If one understands the true meaning of force one will realize however that the choice to convert was still a choice. Under tremendous pressure many did convert, but in the end they were not forced, they chose to convert. They had the ability to remain Zoroastrains and not become Muslim and put up with all the restrictions that entailed. If they decided to convert it was their free will and their choice to do so.
Conflict and cooperation Zoroastrian Subalterns and Muslim Elites in Medieval Iranian Society