The divine messengers are the prophets.[69] They knew that their revelations came from God through a sign which appeared at the beginning of the communication and lasted to the end. The sign was a pillar of cloud or of fire, or an extraordinary bright light, as we learn in the case of Moses. The genuineness of a prophet's message is tested first of all by the nature of the content, and then by his ability to perform miracles. The Israelites would not have believed Moses, notwithstanding his miracles, if he had commanded them to commit murder or adultery. It is because his teaching was found acceptable to the reason that the miracles accompanying it were regarded as a confirmation of Moses's divine mission. The Jewish Law[70] contains three elements, all of which are necessary for effective teaching. First, the commandments and prohibitions, or the laws proper; second, the reward and punishment consequent upon obedience and disobedience; and third, examples of historical characters in which the laws and their consequences are illustrated. But the written law would not accomplish its purpose without belief in tradition. This is fundamental, for without it no individual or society can exist. No one can live by what he perceives with his own senses alone. He must depend upon the information he receives from others. And while this information is liable to error either by reason of the informant being mistaken or his possible purpose to deceive, these two possibilities are eliminated in case the tradition is vouched for not by an individual, but by a whole nation, as in the case of the Jewish revelation. As Saadia's emphasis on tradition, apart from its intrinsic importance for Judaism, has its additional motive in refuting Karaism, so the following discussion against the possibility of the Law being abrogated is directed no doubt against the claims of the two sister religions, Christianity and Mohammedanism.[71] Abrogation of the law, Saadia says, is impossible. For in the first place tradition has unanimously held to this view, and in the second place the Law itself assures us of its permanent validity, "Moses commanded us a law, an inheritance for the assembly of Jacob" (Deut. 33, 4). The law constitutes the national existence of our people; hence as we are assured by the Prophets that the Jewish nation is eternal, the Law must be likewise. We must not even accept the evidence of miracles in favor of a new law abrogating the old. For as we saw before, it was not primarily Moses's miracles that served to authenticate his teaching, but the character of the teaching itself. Now that the law of Moses stood the test of internal acceptability and external confirmation by the performance of miracles, its declaration of permanent validity cannot be upset by any new evidence even if it be miraculous.