If the good spirit was supreme purity and truth, he must originally have created the world in accordance with his nature. Whence then came the injurious, the evil? Had the evil spirit also a creative power? Or was the evil first introduced after the creation of the world? If this was the case, and evil was not always in the world, then it must again disappear from it; if the pure god was the more powerful, he must again overcome the resistance of the evil. Moreover, with the subordination of the light and dark powers to Auramazda and Angromainyu, and their combination into these two forms, an impulse was given which gradually forced the ancient deities into the background. The first point was, to put the latter in the right relation to the new god, who had created heaven and earth, and even these ancient gods. In the same way the old Arian legend of the golden age of Yima must be harmonised with the new doctrine of the creation, and a relation must be established between the sacrificers of the old days, who were without the good law of Zarathrustra, and the latter. The sayings which held in check the evil spirits, and which the reform took from the body of ancient invocations or added to them in their spirit, must be accurately preserved if they were not to lose their force, especially the prayers and incantations which Zarathrustra himself had spoken or was thought to have spoken. Lastly, the mode of worship must be regulated in accordance with the tendencies of the reform. Which and what kind of sacrifices, which invocations and songs of praise were the most efficacious, was a matter which required settling. The old customs of purification so indispensable for keeping at a distance the evil spirits, which the reform, as we ventured to assume, largely increased by new prescripts, must be united with the increased importance attached to truth and purity and combined into a comprehensive rule for the life pleasing to Auramazda. What means were there for wiping out offences against this rule, and sins when committed, for turning aside the anger of Mithra, for expiating falsehood, lying, and deception? We have already indicated (p. 101) how numerous and complicated were the duties of the priesthood arising out of pollution and its removal. The answers which the priesthood of Iran gave to all the questions which successively arose have been collected in the Avesta.