Comentário sobre Deuteronômio 18:22

אשר ידבר הנביא WHEN THE PROPHET SPEAKETH [IN THE NAME OF THE LORD] and says, “This thing will once happen to you”, and you will see that it did not happen, הוא הדבר אשר לא דברו ה׳ THAT IS THE THING WHICH THE LORD HATH NOT SPOKEN — and, therefore, slay him. If, however, you say, “But this refers to one who will prophesy about the future. But suppose one comes and says, ‘Do so and so, and I say this by the command of the Holy One blessed be He’? How, then, can we know whether God has spoken this or not?” The reply is: As regards such a case they have already been commanded that if one comes to thrust thee away from one of the divine commandments, לא תשמע לו “then thou shalt not hearken unto him” (Deuteronomy 13:12), unless you are certain that he is a perfectly righteous man, as, for instance. Elijah at the incident on Mount Carmel, who offered sacrifices on a Bamah (an improvised altar) at a time when offering on Bamoth was forbidden, but who did so in order to fence Israel in against idolatry. Thus all depends on the needs of the time and the necessity of taking preventive measures (סיג) against a breach. With reference to such a case it states, (v. 15) “unto him ye shall hearken” (Sanhedrin 89b; Yevamot 90b).

ולא יהיה הדבר, for when the prophet commands a “new” commandment, unless it is accompanied by a miracle attesting to his authority by G’d to do so, the fact that he failed to produced the promised miracle proves that he is a false prophet. An example of this is mentioned in Joshua in the valley of the river Jordan. (Joshua 3 when Joshua promised miracles and the people crossed the swollen Jordan river with dry feet, the waters having backed up) Also the predicted collapse of the protective wall around Jericho as the result of blasts on the shofar was such a miracle legitimising violating the Sabbath on that occasion. (Joshua 6)
In the case of the prophet Elijah at Mount Carmel, the heavenly fire descending and consuming his offering on the rebuilt altar, as well as the water in the surrounding moat, proved that he had acted with G’d’s approval, was totally authentic. (Kings I 18,38) Concerning the reverse, a prophet being punished for failing to carry out the instructions of his colleague, an example is found in Kings I 20,35-36. Were this not so, why would someone be punished for not inflicting physical hurt on his fellow man?

ולא יהיה הדבר ולא יבא, assuming that repentance and good deeds did not persuade G’d to postpone the decree as He did in response to the repentance and entreaty of Chizkiyah, King of Yehudah whose prayer resulted in his death, announced by the prophet Isaiah, being put on hold for 15 years. (Kings II 20,1-6, as well as Jonah’s prediction that Nineveh was doomed which was rescinded completely, as per Jonah 3,10)