Great oath — That is a solemn oath joined with some terrible execration against the offenders herein. Put to death — Because by refusing to execute the vengeance due to such malefactors, they were justly presumed guilty of the crime, and therefore liable to the same punishment, as was the case of that city that would not deliver up an Idolater dwelling among them, to justice.
Related Commentaries of Judges 21:5
Judges 21:5
5 And the children of Israel said, Who is there among all the tribes of Israel that came not up with the congregation unto the LORD? For they had made a great oath concerning him that came not up to the LORD to Mizpeh, saying, He shall surely be put to death.