The three weeks that begin on the night of the Seventeenth of Tammuz and continue until the Ninth of Av are days of national woefulness. The sages therefore advise being especially careful during this period, for it is a time designated for calamity.
The Chozeh of Lublin senses that the bed which has been prepared for him by the carpenter is not a rejuvenating bed but a bed of lugubriousness and anxiety. From such a bed it is impossible to rise invigorated with a thirst for renewed creativity.
The Mishnah teaches us that the tablets were broken on the 17th of Tamuz as a result of the building of the Golden Calf. Rav Kook explains that if we understand the essence of idolatry we can find a way to mend the broken tablets.
Fast days are occasion for introspection and repentance. After all, we are not fasting over the distant, unrelated past; we are fasting in response to our own present situation. How is it that instead of mourning we remain complacent and indifferent?