Deuteronomy 22:30 - Matthew Poole's English Annotations on the Holy Bible

Shall not take to wife. So this respects the state, and the next branch speaks of the act only. His father's wife; his mother-in-law. See Leviticus 18:8, Leviticus 20:11 1 Corinthians 5:1. His father's skirt, i.e. the skirt of the mother's garment, i.e. the nakedness, which is here called his father's skirt, because his father and mother were one flesh, or because his father alone had the right to uncover it. The phrase is taken from the ancient custom or ceremony of the bridegroom's spreading the skirt of his garment over the bride, to signify his right to her, and authority over her, and his obligation to the marriage duty. See Ruth 3:9 Ezekiel 16:8.