In Deuteronomy 21:10-14, we read the law concerning the marrying of captive women. Deuteronomy 21:10-11 give us this intelligence:

When you go to war against your enemies and the Lord your God delivers them into your hands and you take captives, if you notice among the captives a beautiful woman and are attracted to her, you may take her as your wife.

Deuteronomy 21:10-11 (NIV)

These verses are unambiguous. Israelite men could marry women who were once their enemies. However, in Deuteronomy 7, we’re given this insight:

When the Lord your God brings you into the land you are entering to possess and drives out before you many nations—the Hittites, Girgashites, Amorites, Canaanites, Perizzites, Hivites and Jebusites, seven nations larger and stronger than you— and when the Lord your God has delivered them over to you and you have defeated them, then you must destroy them totally. a Make no treaty with them, and show them no mercy. Do not intermarry with them. Do not give your daughters to their sons or take their daughters for your sons  (emphasis added).

Deuteronomy 7:1-3 (NIV)

Why does the Lord tell the Israelites they couldn’t intermarry with their enemies and then give instructions on what to do when they do intermarry?

In Deuteronomy 7:1-3, seven nations are expressly mentioned: the Hittites, Girgashites, Amorites, Canaanites, Perizzites, Hivites, and Jebusites. These nations collectively referred to as “Canaanites,” were the same nations that did detestable things which is why the Lord gave “their” land to the Israelites. Therefore, the Lord didn’t want the Israelites to intermarry with them because they would teach the Israelites to do those same detestable things. However, the enemies mentioned in Deuteronomy 21:10-14 were not Canaanites. Instead, the enemies in Deuteronomy 21 would be everyone but the Canaanites, so it was okay for the Israelites to marry them.

Therefore, the Lord didn’t tell the Israelites one thing in Deuteronomy 7:1-3 and then something completely different in Deuteronomy 21.