Judges 20:23

And the children of Israel went up and wept before the Lord
until even
The evening of the day in which the battle was fought; not that the whole army went up to Shiloh to the house of God there, but a deputation of them, who lamented their defeat, and the loss of so many lives, but not their sins and transgressions, and particularly the idolatry they had been guilty of:

and asked counsel of the Lord, saying, shall we go up again to battle
against the children of Benjamin my brother?
they seemed to have some doubt, by the loss they sustained, whether they were right in going to war with Benjamin, especially as he was their brother; and therefore the question now is, not who should go up first, which was already determined, but whether they should go at all; and still they do not ask any help of God in battle, nor success, but were depending on their numbers, and the justness of their cause, and therefore neither is promised to them, only they have an answer to their question:

and the Lord said, go up against him;
for Benjamin was certainly in the wrong, and therefore the Israelites are directed to go against him, and they also were not sufficiently chastised, nor thoroughly humbled.