Charles Ellicott Commentary Judges 21:5

"And the children of Israel said, Who is there among all the tribes of Israel that came not up in the assembly unto Jehovah? For they had made a great oath concerning him that came not up unto Jehovah to Mizpah, saying, He shall surely be put to death." — Judges 21:5 (ASV)

Who is there ...? —This verse is anticipatory of Judges 21:8.

They had made a great oath. —Another detail that has been omitted until now. The spirit of this cherem was exactly the same as that which we find in Judges 5:23: Curse you Meroz ... because they did not come to the help of the Lord, to the help of the Lord against the mighty. Now that these victories had been so complete, they probably were sick with slaughter and would not have sought out any defaulters, except as a way to find an expedient to mollify the meaning of their rash oath. We see once more in this narrative both the force derivable from a vow and the folly and wickedness of fierce vows rashly taken in moments of passion. It is obvious that the direct meaning of the vow, taken in connection with the curse they had placed on the Benjamites, was to annihilate the tribe.