Our mourning and our tears will rebuild the Beis HaMikdash. The Shlah HaKadosh (Masechta Taanis, Ner Mitzvah, #33) writes that we don't mourn on Shabbos because mourning builds the Beis HaMikdash, and it is forbidden to build the Beis HaMikdash on Shabbos.
It states (Tehillim 147), ישראל נדחי 'ה ירושלים בונה יכנס, "Hashem builds Yerushalayim, He will gather in the dispersed of Yisrael." The Chasam Sofer zy'a (Drush 7th Av, 5599) asks that it seems that the pasuk should state in the future tense 'ה ירושלים יבנה, "Hashem will build Yerushalayim." Why is it written in the present tense, ירושלים בונה, that Hashem is building the Beis HaMikdash now?
Chazal tell us that the third Beis HaMikdash will come down from heaven fully built up (see Rashi on Rosh Hashanah 30. צ"ל ה"ד). Hashem is building the Third Beis HaMikdash in heaven, and the construction materials are our tears and mourning. For two thousand years, we have mourned and cried for the Churban. Hakadosh Baruch Hu takes all those tears and mourning, and He builds the third Beis HaMikdash in heaven with them, brick by brick, stone by stone. When it is completed, it will come down from heaven.
The Gemara (Makos 24) says: Rabban Gamliel, Reb Elazer ben Azaryah, Reb Yehoshua, and Reb Akiva traveled to Yerushalayim. When they came to Har HaBayis, they saw foxes coming out of the Kodesh Kodoshim. Rabban Gamliel, Reb Elazer ben Azaryah, and Reb Yehoshua cried. Reb Akiva laughed. They asked R’ Akiva, "Why are you laughing?" Reb Akiva asked, "Why are you crying?" They said, "The place about which is states יומת הקרב והזר (that only kohanim may go there and anyone else will die) has foxes prancing about it. Shouldn't we cry?" Reb Akiva replied, מצחק אני לכך, "That is precisely why I'm laughing." Reb Akiva explained to them that when he saw the actualization of the prophecies of the destruction, he felt reassured that the prophecies of redemption would transpire. From Reb Akiva's words, מצחק אני לכך it seems that he was laughing because they were mourning.
Rebbe Yisrael of Tchortkov zt'l explains that he was happy that Yidden were mourning over the Churban because those tears would build the third Beis HaMikdash. This is as the Zohar (vol.2 p.12:) tells us, "The redemption of Bnei Yisrael depends solely on crying."
Beneβits of Mourning
Many benefits come from mourning. Reb Chaim Palagi (Moed l'Kol Chay, Av, #61) writes, "When one mourns for the Churban Beis HaMikdash, his sins are forgiven, he will live a long life, his children won't die in his lifetime, and his children will live long." Rebbe Pinchas Koritzer zt'l (Imrei Pinchas 404) says, "Tisha b'Av atones for sins because people are very broken. This is why after Tisha b'Av, we feel slightly similar to how we feel after Yom Kippur."
The Chasam Sofer zt'l said that those who cry for the Churban merit good children. (Therefore, as one mourns, it is an auspicious time to daven for your children's success in Torah and yiras Shamayim.)
The Kav HaYashar (ch.93) writes, "I received a true kabbalah: Whoever is always distressed about the galus HaShechinah will merit the crown of Torah."
Reb Yehudah of Asad zt'l would save the tears that fell from his eyes at Tikun Chatzos and give them to bachurim at risk of being drafted into the army. This segulah helped them (Toldos Shmuel, as told by the testimonies of Reb Yosef Tzvi Dushinsky zt'l and others).
Tana d'Bei Eliyahu (Rabba 20 אחת פעם ה"ד) tells that the nations פרס and מדי came to the...
