Deuteronomy 21:13, commentary and pictures

The law requires that a captive woman taken to be a wife first put off her captive clothing, remain in the captor's house, and bewail her father and her mother for a full month, and only after that may he go in to her and become her husband and she his wife. That month of mourning marked her final separation from her idolatrous family, and together with shaving her head and trimming her nails it signified that she had become a proselyte to the Jewish religion to be received into the Israelite household and treated as one of the people.

She was not to be taken for lust or for immoral use, a misuse for which Israel was punished, but was to be brought into the house and made a wife and member of the family, and uncorrupted girls kept alive under this rule could live as servants reared in virtue in a life many times better than in their own nation. She was not to be treated simply as property or a slave, and if her captor afterward rejected her he might not sell her or make merchandise of her because he had humbled her, a dealing that was just and far better than slavery. This same rule of humane treatment applies to the spared female children in Numbers 31:18, who were kept partly for slaves and partly for wives.

The law was the very best God could do with Israel at that time without destroying their free will, as He does with every nation, and it shows a regard for women and a humanity toward slaves and captives far above all foreign and heathen nations around Israel. It was light and salvation in darkness leading on to still greater light, with customs far ahead of surrounding nations, so that slaves in Israel were many times better off than free men and women in other lands. It parallels the summons to the daughter to hearken and consider that is addressed to the queen in gold of Ophir standing at the king's right hand.