The Gemara (Shabbos 31) says that when a person is niftar, one of the first questions that heaven will ask him is צפית לישועה, "Did you hope for Moshiach?"
Reb Yaakov Emdin zt'l (Siddur Beis Yaakov, Tisha b'Av 6:16) writes, "If our only sin were that we didn't mourn over Yerushalayim, it would be sufficient to prolong our galus. In my opinion, this is the primary cause of all the terrible destructions – beyond comprehension – that befall us in galus. We are pursued and don’t have peace… all because the mourning has left our hearts."
In particular, we should mourn the churban Beis HaMikdash during the Three Weeks. The Magen Avraham (551:45) writes, "The Arizal taught that one should mourn during these days [of the Three Weeks] after midday and cry for around a half-hour." Generally, Tikun Chatzos is said after midnight, but these days, it can also be recited in the afternoon.
In the Chasam Sofer's yeshiva, during the Three Weeks, they would recite Tikun Chatzos together and mourn the churban every afternoon. Generally, the tzaddik, Reb Fishel Sofer zy'a, was the chazzan, and he would cry bitterly as he said it. One day, Reb Fishel wasn't in yeshiva, and a young bachur with a sweet voice was chosen to lead Tikun Chatzos. This bachur didn’t cry; his recitation sounded more like a yom tov tefillah than kinos. When he finished, the Chasam Sofer said, "We must verify whether this bachur doesn't belong to Shabtai Tzvi's sr'y group. Because how can one relate to the churban Beis HaMikdash with such ease and comfort?"
During the Three Weeks, a certain tzaddik visited the Sfas Emes of Gur zt'l. "What brings you here?" the Sfas Emes asked. "I know that you live very far away from here!"
"My family's tradition is to travel during the Three Weeks," the tzaddik explained. "Hashem is, kivayachol, in galus, so it is our custom to go into galus during this period."
The Sfas Emes replied, "The main thing is to remember that we aren't home." The Sfas Emes rarely traveled, but he frequently reminded himself that he wasn’t home. We aren't where we ought to be. This realization should never leave our consciousness.
- 8. Reb Yosef Chaim Sonnenfeld zt'l, who studied in the Ksav Sofer's yeshiva in Pressburg, said, "I once heard two women of Pressburg speaking. One asked the other, 'What did you prepare for lunch today.' 'I prepared beans,' she said. 'And what will you make tomorrow?' The woman replied, 'Sha! Sha! אל תפתח פה לשטן. [Don't even consider that tomorrow will be a regular day.] But if chas v'shalom Moshiach doesn't come, I will cook potatoes.' Reb Yosef Chaim repeated this story, to show how simple people in Pressburg awaited and believed in the coming of Moshiach.
- A businessman came to the Apter Rav zt'l to ask for business advice. The Rebbe gave him wise counsel, and then the rebbe emitted a deep moan and said with a broken heart, "A great tragedy happened today." "What happened?" the man asked. "We didn’t bring the korban tamid today…" the Apter Rav cried copiously.
- Someone came to the Kotzker Rebbe zt'l, complaining that his son-in-law had become a Kotzker chassid. He told the rebbe that his daughter was very upset about this, and the father cried, "If one has a heart, how could it not burst from pain because of my daughter's sorrow?" The rebbe replied, "If one indeed has a heart, how could it not burst from pain because of the churban Beis HaMikdash."
- 9. The Chasam Sofer said that whoever mourns over the Beis HaMikdash during the Three Weeks will merit good children.