The worshipper of Auramazda must preserve his purity by good thoughts, words, and works; truth is required in thinking, speaking, and acting; uprightness and honesty in all the relations of life; the sacredness of promises and pledges, and solemn assurances, at which Mithra is summoned to bear witness. It is an old function of the god which appears here. He is the guardian of the word, and the compact. "Mithra is twenty-fold between friends and kinsmen, thirty-fold between tradespeople, forty-fold between companions who live together, fifty-fold between man and wife, sixty-fold between associates in sacrifice, seventy-fold between scholar and teacher, eighty-fold between step-son and step-parents, ninety-fold between brothers, a hundred-fold between son and father." "Miserable are the houses, without descendants the dwellings, inhabited by those who deceive Mithra. Miserably does the cloven-footed cow go on the wrong path, which is oppressed by the burden of Mithra-deceiving men."[342] In accordance with this view deception is in the eyes of the law the worst offence; worse than robbery or theft. Evil-speaking and calumny also are, according to the Vendidad, "lies and sins" against Mithra. The gravest offence of this kind is the calumny by which "a pure man" is disparaged "with a man of another religion," for this sin is committed with full knowledge, and by a man's own intelligence; and the worst of all lies is teaching a false law. "One who teaches such a law," says the Vendidad, "does no better than if he killed a thousand horses, slew the men in a village inhabited by worshippers of Auramazda, or carried off the cows on the wrong way."[343]