Deuteronomy 18:21 - Testing prophecy's divine origin?

Deuteronomy 18:21 - דברים 18:21

Hebrew Text

וְכִי תֹאמַר בִּלְבָבֶךָ אֵיכָה נֵדַע אֶת־הַדָּבָר אֲשֶׁר לֹא־דִבְּרוֹ יְהוָה׃

English Translation

And if thou say in thy heart, How shall we know the word which the Lord has not spoken?

Transliteration

V'chi tomar bilvavecha eicha neida et-hadavar asher lo-dibero Adonai.

Hebrew Leining Text

וְכִ֥י תֹאמַ֖ר בִּלְבָבֶ֑ךָ אֵיכָה֙ נֵדַ֣ע אֶת־הַדָּבָ֔ר אֲשֶׁ֥ר לֹא־דִבְּר֖וֹ יְהֹוָֽה׃

Parasha Commentary

Context in Sefer Devarim

This verse appears in Devarim (Deuteronomy) 18:21, within a section discussing the criteria for distinguishing true prophets from false ones. The Torah anticipates the people's concern about verifying prophetic authenticity, as false prophets could lead them astray.

Rashi's Explanation

Rashi (Rabbi Shlomo Yitzchaki) comments that this verse reflects a legitimate concern: how can one discern whether a prophet's words are truly from Hashem? He explains that the Torah provides the answer in the following verse (18:22): if the prophecy does not come to pass, it was not spoken by Hashem. Rashi emphasizes that this applies specifically to prophecies of tov (good) or ra'ah (calamity), not to conditional prophecies where repentance could alter the outcome.

Rambam's Perspective

In Hilchot Yesodei HaTorah (Laws of the Foundations of the Torah 10:4), the Rambam (Maimonides) elaborates on the signs of a true prophet. He states that a prophet must:

  • Be known for wisdom and piety before claiming prophecy
  • Speak only in accordance with Torah principles
  • Have his predictions come true without fail

The Rambam notes that even if a prophet performs miracles, if he contradicts Torah law, he is false (based on Devarim 13:2-6).

Talmudic Insights

The Talmud (Sanhedrin 89a) discusses this verse in the context of the nevi'ei sheker (false prophets). It explains that true prophets speak with humility ("perhaps Hashem will grant...") while false prophets speak with certainty ("Hashem said..."). The Sages derive from our verse that doubt about a prophet's authenticity is natural and requires careful verification.

Midrashic Interpretation

The Sifrei (Devarim 18:21) connects this verse to the broader theme of emunat nevi'im (belief in prophets). It teaches that Hashem provided clear guidelines specifically because He wants the Jewish people to follow true prophets, not to be misled by imposters. The Midrash emphasizes that this concern demonstrates the people's wisdom in wanting to properly serve Hashem.

Practical Halachic Application

Based on these sources, later halachic authorities (such as the Sefer HaChinuch Mitzvah 516) derive several principles for evaluating prophets:

  • A prophet cannot introduce new mitzvot or alter existing ones
  • His personal conduct must be beyond reproach
  • The content of his message must align with Torah values
  • His predictions must materialize exactly as stated (for unconditional prophecies)

📚 Talmud Citations

This verse is quoted in the Talmud.

📖 Sanhedrin 89a
The verse is referenced in a discussion about false prophets and how to discern whether a prophecy is truly from God.

Frequently Asked Questions

Q: What does Deuteronomy 18:21 mean?
A: Deuteronomy 18:21 addresses the concern of how to distinguish between a true prophet and a false one. The Torah provides criteria to test a prophet's authenticity, such as whether their predictions come true (Deuteronomy 18:22) and whether their teachings align with Torah law (Deuteronomy 13:2-6). Rashi explains that this verse reassures the people that Hashem gives clear signs to identify false prophets.
Q: Why is Deuteronomy 18:21 important?
A: This verse is important because it teaches us to be cautious and discerning when someone claims to speak in Hashem's name. The Talmud (Sanhedrin 89a) discusses the severe consequences of false prophecy, emphasizing the need to verify a prophet's legitimacy. The Rambam (Hilchot Yesodei HaTorah 10:1-4) outlines the laws regarding prophecy, stressing that a true prophet must uphold Torah principles without contradiction.
Q: How can we apply Deuteronomy 18:21 today?
A: While we no longer have prophets like in biblical times, the principle of discernment remains relevant. We must evaluate religious teachings and leaders based on their adherence to Torah and halacha (Jewish law). The Midrash (Sifrei Devarim 18:21) teaches that truth in Torah is consistent and unchanging, so any claim that contradicts established Torah teachings should be questioned.
Q: What does 'How shall we know the word which the Lord has not spoken?' teach us?
A: This question reflects a healthy skepticism and desire for clarity in spiritual matters. The Torah encourages us to seek truth and not blindly accept claims of prophecy. Rashi and other commentators emphasize that Hashem provides guidance—through Torah, mitzvot, and rabbinic tradition—to distinguish truth from falsehood.

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