A common misinterpretation applies this verse to forbid all marriages to a deceased spouse's sibling, overlooking the levirate marriage provision in Deuteronomy 25 where a man is required to marry his brother's widow to preserve the family line, or assumes the 'childless' curse is a literal ongoing punishment today rather than a specific consequence under Mosaic law for living brothers' wives.
Leviticus 20:21
King James Version (1769)
21 And if a man shall take his brother’s wife, it is an unclean thing: he hath uncovered his brother’s nakedness; they shall be childless.
Leviticus 20:21 underscores God's command against a man taking his brother's wife as an act of impurity that dishonors familial bonds and violates sexual purity laws within the Israelite community, resulting in the divine judgment of childlessness to emphasize the seriousness of such incestuous unions and maintain holiness among God's people.