Being childless brought public shame in society. People considered it a judgment from God (see Genesis 30:1–2; Deuteronomy 7:14).
What situation do these verses describe? Leviticus 18:14,16 already discuss sexual relations with an uncle’s wife or sister-in-law. Deuteronomy 22:22 addresses adultery that results in death for both involved. If the woman was a widow without a male heir, the law of levirate marriage could apply (Deuteronomy 25:5–6; see study note on Leviticus 18:16).
Since those situations do not seem to apply, this law probably refers to marrying an aunt or a sister-in-law after her divorce. John the Baptist apparently used this law to condemn Herod Antipas’s marriage to Herodias (see Mark 6:17–29).