Three Weeks
Shabbos Nachamu
The doubled × ×—×ž×• of the haftorah answers to the two churbanot, but the deeper question is why two separate comforts are needed when the third Beit Hamikdash will resolve both losses at once. The answer distinguishes the first Temple's higher level of Shechinah, a kedushah that came מלמעלה למטה and was built by tzadikim, from the second Temple's greater staying power, built מלמטה למעלה by baalei teshuvah and so more absorbed into the world despite a lower revelation. The third Beit Hamikdash is described as combining both maalos, a Shechinah as high as the first and a permanence beyond the second, which is the full double comfort × ×—×ž×• × ×—×ž×• is promising.
The Chassidic Approach to the Three Weeks and Tisha B'Av
Explains the Chassidic view that Tisha B'Av's destruction is itself a form of redemption, comparing it to a seed that must rot before it can grow, and connects it to the ultimate revelation of the Third Beis Hamikdash.