What does Judges 21:12 mean?
The Israelites have conducted another massacre of their own people. Like the previous bloodshed in Benjamin (Judges 20:47–48), this is not commanded by God; it's Israel's excessive attempt to correct their own mistakes. A force of soldiers were sent to slaughter every man, child, and married woman among the peoples of Jabesh-gilead. They kill everyone except four hundred unmarried young women. These are taken to Shiloh, to be given as brides to the surviving six hundred men of Benjamin. The justification for this is an oath made before the war with the tribe of Benjamin (Judges 20:11–13): to put to death whatever people did not send representatives to the assembly at Mizpah (Judges 21:5). The practical reason for this drastic step is partially explained in this verse.The Israelites believe they have found a loophole in an unwise promise they made: to not marry any of their daughters to the men of Benjamin (Judges 21:1). The people of Jabesh-gilead did not attend the assembly and never took that oath. In that way, giving these young women to the Benjaminites is not a violation of that specific vow. Of course, the people of Israel are blatantly ignoring the moral contradiction at the heart of this decision. If they were right to destroy everyone in Jabesh-gilead, they should have also killed these young women. If those young women could be spared within the bounds of the oath, then all the people could have been spared.
The truth is that Israel wants to prevent the tribe of Benjamin from dying off because of their own poor decisions and unwise promises. None of this appears to have been directed by the Lord.