a man shall This is to be understood as referring to the case of a stepmother. A man in his old age may have married a young woman, and on his dying, his son by another, or a former wife, may desire to espouse her; which is forbidden.

Leviticus 27:20 And if he will not redeem the field, or if he have sold the field to another man, it shall not be redeemed any more.

Leviticus 18:8 The nakedness of your father's wife shall you not uncover: it is your father's nakedness.

Leviticus 20:11 And the man that lies with his father's wife has uncovered his father's nakedness: both of them shall surely be put to death...

1 Corinthians 5:1,13 It is reported commonly that there is fornication among you, and such fornication as is not so much as named among the Gentiles...

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Ruth 3:9 And he said, Who are you? And she answered, I am Ruth your handmaid: spread therefore your skirt over your handmaid...

Ezekiel 16:8 Now when I passed by you, and looked on you, behold, your time was the time of love; and I spread my skirt over you...