Deuteronomy 21 · a question people ask
Why does the law give rules for taking a captive as a wife instead of forbidding it?
The chapter doesn't say why. It says what the rules were. The man was to "bring her home to your house" (21:12). "She shall take off the clothing of her captivity, and shall remain in your house, and bewail her father and her mother a full month", and only "After that" could she become his wife (21:13). If he had "no delight in her", "you shall let her go where she desires; but you shall not sell her at all for money. You shall not deal with her as a slave, because you have humbled her" (21:14). Readers agree on what the rules required and that the text gives no reason for allowing the marriage. They read the reason for the law in more than one way.
How Christians read it
Where Christians differ, Favor sets out the main views side by side and doesn't pick one.
Allowed because of hard hearts
Jesus said of divorce, "Moses, because of the hardness of your hearts, allowed you to divorce your wives, but from the beginning it has not been so" (Matthew 19:8). Those words are about divorce, not this law; Jesus doesn't apply them here. Those who hold this view read 21:10-14 the same way: as limits the law set around a man who had taken a captive (21:10-11), like the full month (21:13) and the ban on selling her (21:14), not a picture of what God made people for "from the beginning".
Matthew 19:8 · Deuteronomy 21:10-14
Terms the LORD set for Israel
Those who hold this view read the law as the LORD's own terms for Israel in this case, and point to what the terms required of the man: a full month for her to "bewail her father and her mother" (21:13), the name "your wife" (21:13), letting her "go where she desires" if he sent her away, and no selling her or dealing with her "as a slave" (21:14). They note that the law gives its own reason for that last command: "because you have humbled her" (21:14).
Deuteronomy 21:13-14