4 and lead it down to a valley that has not been plowed or planted and where there is a flowing stream. There in the valley they are to break the heifer's neck.

Matthew Henry's Commentary on Deuteronomy 21:4

Commentary on Deuteronomy 21:1-9

(Read Deuteronomy 21:1-9)

If a murderer could not be found out, great solemnity is provided for putting away the guilt from the land, as an expression of dread and detesting of that sin. The providence of God has often wonderfully brought to light these hidden works of darkness, and the sin of the guilty has often strangely found them out. The dread of murder should be deeply impressed upon every heart, and all should join in detecting and punishing those who are guilty. The elders were to profess that they had not been any way aiding or abetting the sin. The priests were to pray to God for the country and nation, that God would be merciful. We must empty that measure by our prayers, which others are filling by their sins. All would be taught by this solemnity, to use the utmost care and diligence to prevent, discover, and punish murder. We may all learn from hence to take heed of partaking in other men's sins. And we have fellowship with the unfruitful works of darkness, if we do not reprove them.