Why should one not listen to the Navi who substantiates his prophecy with a miracle?
Ramban: Because Hashem, whom we saw firsthand at Yetzi'as Mitzrayim is Master of the world, 1 and that there is no other god like Him, commanded us 2 at Ma'amad Har Sinai, not to worship any deity other than Himself. 3
Seforno: Because, since part of his prophesy is meant to take us away from Hashem, it is clear that there is no truth in any of his words, and his miracle was based on witchcraft or something similar; nor did he prophesy or dream at all, but concocted his ?prophecy? or his dream off his own bat ? in order to veer us away from Hashem.
What is the objective of the test?
Seforno: To demonstrate our hatred towards the Navi Sheker who is speaking against Hashem, thereby proving that we love Hashem, thereby sparking off a reciprocal reaction from Hashem, who will showers the world with goodness.
Oznayim la'Torah: To demonstrate to the people that they do not love Hashem 'be'Chol Levavam u've'Chol Nafsham'. 1
What is the point of the test, seeing as Hashem knows what is in is person's heart?
Ramban (in Vayeira, Bereishis, 22:1): It is to convert the potential into action - in order to reward the Tzadik 1 for passing the test.
Ramban: In fact, Hashem only tests Tzadikim - because He loves them - as the Pasuk writes in Tehilim, 11:5 "va'Hashem Tzadik Yivchan".
Why does the Torah insert the (otherwise superfluous) words "Ha'yishchem Ohavim es Hashem ? be'Chol Levavchem u've'Chol Nafsh'chem"?
Oznayim la'Torah: The Torah is speaking about a case where the Navi instructs the people to serve Avodah Zarah in order to bring rain - and they follow his instructions and it does indeed rain. Based on the Pesukim in 'Vehayah Im Shamo'a', Hashem sends rain if the people 'love Him with all their heart and with all their Soul'. Consequently, the fact that it requires the Navi Sheker to bring rain is proof that they do not.
