Halakha Yeremia 5:25: Mishneh Torah, Fasts

And this thing is from the ways of repentance. For when a trouble comes and they yell out about it and sound [trumpets], everyone will know that it was because of their evil deeds that this bad was done to them. As it is stated (Jeremiah 5:25), "It is your iniquities that have diverted, etc." And this is what will cause them to remove the trouble from upon them.