When the Jews in Russia were suffering from persecutions, the Chofetz Chaim convened a meeting of rabbis to enact a public fast due to the situation. All the rabbis signed and the Chofetz Chaim asked Rav Chaim Brisker to add his signature too. However, Rav Chaim would not sign, and the Chofetz Chaim sent a messenger to find out why. Rav Chaim explained that the main purpose of a fast is to open up the heart to repentance, as it says (Taanis 16a), “Neither sackcloth nor fast is effective, but only repentance and good deeds”, and as the prophet has already stated expressly (Yeshaya 58:6), “Is not this the fast that I have chosen? To loose the fetters of wickedness, to undo the bands of the yoke, and to let the oppressed go free, and that you break every yoke?” Furthermore, the Rambam says (H. Ta’anis 1:17) that when the Beis Din enact a public fast they must sit together and examine the deeds of the town’s inhabitants, and warn them and remove any obstacles from the generation. Only then does the fast serve a purpose. Hence, Rav Chaim concluded, the rabbis must first meet in order to discuss what needs to be amended based on the situation of the generation, and only subsequently enact a fast.
(Excerpted from Rabbi Moshe Sternbuch’s public letter on Corona of 23 Adar 5780)