מוסר אויף ישעיהו 66:10

Therefore, one should concern himself and weep because of the Torah which is forgotten and should lament for those who revere God, Blessed be He, and have been rejected by men, and should complain bitterly over the little piety that exists and over Israel, the people of the Lord, trodden under foot, and he should raise Jerusalem over his greatest joy and may he merit to behold her joy, as it is written : "Rejoice for joy with her; all ye that mourn for her" (Is. 66:10).

Therefore it is fitting for every person of the seed of Israel to lament and weep over the magnitude of the destruction and the yoke of the exile. Moreover, how fitting it would be if they would all mourn and cast themselves upon the ground to wallow in the dust and ashes. This is especially appropriate from the seventeenth of Tammuz onward, for that is a period of sadness during which we are obliged to mourn, and all the more so on [the last day of that period,] the Ninth of Av, which is a day for weeping and sorrow. But in many countries, on account of our many sins, I have seen a great breach on the part of those who come to the synagogue. Not only do they neglect to recite the elegies with weeping and bitterness, but they actually engage in jocularity and levity, rejoicing out loud and conducting themselves as if it were [the festival of] Simchas Torah! They have forgotten that their end will be very bitter and their punishment very great. None of those people will merit witnessing the consolation of Israel when our Moshiach arrives. It is the responsibility of the rabbis and leaders of the generation and the judges of Israel to rebuke these sinners who rejoice on a day of suffering and weeping. They must be fined and it is even appropriate to subject them to ostracism. But if a person mourns continually over the destruction of the Holy Temple and the length of the exile and experiences pain over the suffering of Israel, he will merit witnessing their consolation when our Moshiach arrives. He will also witness the vengeance of Hashem of Hosts and will rejoice in the rebuilding of the Temple and the holy city of Jerusalem. For it states, “Rejoice with her in gladness, all who mourned over her” (Yeshayahu 66:10). Amein. — Based upon the words of my teacher and mentor, Rabbi Yosef, z”l.