Ahura Mazda is the law-giver and judge
Ahura Mazda is the law-giver and judge:
With the creation of man Ahura Mazda has ordained laws for the rightful conduct of his life (Y46.15; 51.19). The great mission of the prophet is to acquaint mankind with these and to lead all to see for themselves with their intelligence that their welfare depends on the faithful adherence to them. He exhorts his hearers to give a careful hearing to his words, understand with clear discernment what he tells them, and, with the discreet exercise of the freedom of the will, with which Ahura Mazda has endowed them, make their own choice of conduct (Y30.2). The divine law-giver has established the moral order in the beginning of the world (Y46.6). He has ordained the commandments of reward and retribution to the righteous and the wicked, and Zarathushtra asks his followers to keep them in mind and live lawful lives so that they may thereby win felicity for themselves (Y30.11; 45.7; 51.6). Every man and every woman that lives this earthly life will have to stand at the reckoning one day to receive his or her own desert, and Zarathushtra teaches them all the laws of the requitals of human conduct in which Ahura Mazda himself has instructed him (Y31.14). Ahura Mazda is the lord who knows and watches and judges the deeds of mortals (Y29.4; 31.8). He holds the destinies of mankind in his hands and apportions reward and retribution unto the righteous and the wicked (Y43.4, 5). The righteous souls will live in the abode of Ahura Mazda (Y30.10; 48.7; 49.10). He punishes the wrong-doers just as he rewards the righteous, but he shows compassion also and forgives when the penitent sinner casts himself on his mercy (Y30.2).
Source : History of zoroastrianism, Chapter V