This background information tells the reader about the promise that the Israelites made before the battle with the Benjamites. (See: [[rc://en/ta/man/translate/writing-background]])
The people of Israel used this rhetorical question to express their deep sadness. This question can be translated as a statement. AT: "Oh Yahweh, we are so sad that one of the tribes of Israel has been completely destroyed." (See: [[rc://en/ta/man/translate/figs-rquestion]])