A committed relationship
לא תשמע אל-דברי הנביא ההוא או אל-חולם החלום ההוא כי מנסה יקוק אלקיכם אתכם לדעת הישכם אהבים את-יקוק אלקיכם בכל-לבבכם ובכל-נפשכם
Do not listen to that prophet, or the one who dreamed a dream, for Hashem your G-d is testing you, to know if you really love Hashem your G-d with all your heart and all your soul
The Torah introduces the interesting topic of the false prophet. The Torah declares that after Moshe is gone, there will be new prophets to lead and inspire the people. However, amongst these prophets there will be charlatans who prophesize falsely. Worse of all, some of them will be miracle performers. They will at first appear to be real prophets, accurately predicting real events which will occur. What makes them false is they will command things in the name of Hashem which He never commanded.
The Torah warns us that if these prophets tell us to worship idols, we are to realize that they are a fraud. Hashem would never send His prophets to tell us to worship idols. The fact that these “prophets” perform miracles is irrelevant. Hashem only gave them powers to perform miracles as a way of testing us. He wants to see, so-to-speak, how loyal we truly are. At first glance, this “test” seems rather preposterous. Why is it a lack of loyalty to Hashem, if from our perspectives His very own prophets are telling us to worship idols? Isn’t it more loyal to listen to His prophets? Also, why is it specifically idol worship with which we are to ignore the command of a prophet?
One of the early halachic decisors, the Maharik, was asked regarding a woman who cheated on her husband. Normally, when a wife is unfaithful, she becomes forever forbidden to her husband. However, in this particular case, she thought it was permitted to be involved in extramarital relations. Would we say then that she’s forbidden? She didn’t know adultery was a grave transgression. He responded that although she committed no sin against Hashem, as her intent wasn’t to rebel against Him, she is forbidden. The Torah, when it describes an unfaithful wife, doesn’t mention it as a crime against Hashem. It describes it as a crime against the husband. Adultery by definition shows a lack of commitment to the marriage. Since, at the end of the day, she wasn’t faithful to him, she is forever forbidden to him.
Perhaps we can apply the same logic to the false prophet. Idol worship is unlike any other transgression in the Torah. It is akin to being unfaithful to Hashem in the relationship we have with Him. Other transgressions, if Hashem tells us through His prophets to commit them, can’t be considered doing something wrong. However, if a prophet tells us to commit idol worship, if we truly loved Hashem with all of our hearts and souls, it wouldn’t be possible for us to listen. If someone would follow such a prophet, it would be proof that there was as lacking in their relationship with Hashem. As such, a false prophet is the perfect test to gauge our level of commitment to Hashem.
 Based on Divrei Shaul to Deuteronomy 13:4 Tinyana, written by the author of the Shoel UMeishiv
 Deuteronomy loc. cit.
 Teshuvos Maharik § 167
 Yevamos 56b; Kesubos 51b
 Numbers 5:12