King James Version

What Does Deuteronomy 18:21 Mean?

Deuteronomy 18:21 in the King James Version says “And if thou say in thine heart, How shall we know the word which the LORD hath not spoken?” — study this verse from Deuteronomy chapter 18 with commentary, cross-references, and original Hebrew word analysis.

“And if thou say in thine heart, How shall we know the word which the LORD hath not spoken?”

Deuteronomy 18:21 · KJV

Context

19

And it shall come to pass, that whosoever will not hearken unto my words which he shall speak in my name, I will require it of him.

20

But the prophet, which shall presume to speak a word in my name, which I have not commanded him to speak, or that shall speak in the name of other gods, even that prophet shall die.

21

And if thou say in thine heart, How shall we know the word which the LORD hath not spoken?

22

When a prophet speaketh in the name of the LORD, if the thing follow not, nor come to pass, that is the thing which the LORD hath not spoken, but the prophet hath spoken it presumptuously: thou shalt not be afraid of him.

Read Deuteronomy 18 full chapter

Commentary

KJV Study Commentary
And if thou say in thine heart, How shall we know the word which the LORD hath not spoken? This verse addresses a critical question for God's covenant people: how to discern true prophecy from false. The Hebrew construction suggests an internal dialogue—ki tomar bilvavekha ("if/when you say in your heart")—acknowledging that this question naturally arises in the mind of the thoughtful believer facing competing prophetic claims.

The verb yada (יָדַע, "know") appears here in its causative form, emphasizing acquired knowledge through testing and verification. God doesn't expect blind acceptance but provides discernment criteria. The phrase "the word which the LORD hath not spoken" uses lo dibber (לֹא דִבֶּר), the emphatic negative—absolutely not spoken by Yahweh. This implies that false prophecy isn't merely mistaken human opinion but dangerous deception that claims divine authority without divine origin.

Context is crucial: verse 22 provides the answer—if a prophet's prediction doesn't come to pass, God didn't speak it. But earlier verses (18-20) add theological criteria: true prophets speak only in Yahweh's name, deliver messages consistent with revealed truth, and face divine judgment for presumption. The test is both predictive accuracy and theological fidelity. Moses anticipated Israel's need for ongoing prophetic guidance while protecting them from deception—a pattern pointing ultimately to Christ, the Prophet greater than Moses (Deuteronomy 18:15-19), whose words are life itself.

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Historical & Cultural Context

This passage appears in Moses' final addresses to Israel before entering Canaan (Deuteronomy 12-26 contains the detailed covenant stipulations). Israel would soon encounter Canaanite culture saturated with divination, necromancy, augury, and pagan prophecy (verses 9-14 list these forbidden practices). The ancient Near East had numerous prophetic figures—from Mesopotamian baru priests who read omens to Egyptian oracle-givers who claimed divine knowledge.

Unlike pagan prophecy rooted in manipulation, Israel's prophetic office was revelatory—God disclosed His will through chosen spokespersons. The high stakes required clear discernment standards since false prophets could lead the nation into covenant violation and divine judgment. Historical examples abound: Jeremiah confronted Hananiah's false optimistic prophecy (Jeremiah 28), while Micaiah stood alone against 400 false prophets before Ahab (1 Kings 22).

In Moses' era, the memory of Balaam's attempted cursing (Numbers 22-24) and the recent apostasy at Baal Peor (Numbers 25) underscored prophecy's power for good or evil. This law protected Israel's unique covenantal relationship with Yahweh by establishing objective verification methods—preventing prophetic authority from becoming arbitrary or manipulative. The question in verse 21 reflects the practical wisdom needed to navigate competing religious claims while maintaining exclusive loyalty to Yahweh.

Reflection Questions

  1. What criteria does Scripture provide for testing modern claims of prophetic revelation or divine guidance?
  2. How do we balance openness to God's ongoing work with wise discernment against deception?
  3. In what ways might we be tempted to accept teaching that claims divine authority without proper verification?
  4. How does this passage inform our approach to evaluating preachers, teachers, and spiritual leaders today?
  5. What role does fulfilled prophecy play in confirming Scripture's divine origin and authority?

Original Language Analysis

Hebrew · 11 words
וְכִ֥י1 of 11
H3588

(by implication) very widely used as a relative conjunction or adverb (as below); often largely modified by other particles annexed

תֹאמַ֖ר2 of 11

“And if thou say”

H559

to say (used with great latitude)

בִּלְבָבֶ֑ךָ3 of 11

“in thine heart”

H3824

the heart (as the most interior organ)

אֵיכָה֙4 of 11
H349

how? or how!; also where

נֵדַ֣ע5 of 11

“How shall we know”

H3045

to know (properly, to ascertain by seeing); used in a great variety of senses, figuratively, literally, euphemistically and inferentially (including o

אֶת6 of 11
H853

properly, self (but generally used to point out more definitely the object of a verb or preposition, even or namely)

הַדָּבָ֔ר7 of 11

“the word”

H1697

a word; by implication, a matter (as spoken of) or thing; adverbially, a cause

אֲשֶׁ֥ר8 of 11
H834

who, which, what, that; also (as an adverb and a conjunction) when, where, how, because, in order that, etc

לֹֽא9 of 11
H3808

not (the simple or abs. negation); by implication, no; often used with other particles

דִבְּר֖וֹ10 of 11

“hath not spoken”

H1696

perhaps properly, to arrange; but used figuratively (of words), to speak; rarely (in a destructive sense) to subdue

יְהוָֽה׃11 of 11

“which the LORD”

H3068

(the) self-existent or eternal; jeho-vah, jewish national name of god

Study Guide

Historical Context

This verse is found in the book of Deuteronomy. Understanding the historical and cultural background helps illuminate its meaning for the original audience and for us today.

Theological Significance

Deuteronomy 18:21 contributes to our understanding of God's character and His relationship with humanity. Consider how this verse connects to the broader themes of Scripture.

Cross-References

Verses related to Deuteronomy 18:21 from Treasury of Scripture Knowledge

1 John 4:1-31 Thessalonians 5:24Revelation 2:2

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