When it comes to the day the walls were breached we commemorate only the date for the second Beit HaMikdash (17 Tammuz). When it comes to the siege, why do we only commemorate when it occurred during the time of the first Beit HaMikdash?
Why does the Navi call the fasts not by the day but by the month (the fast of the 10th month, etc.)
Why does the Avudraham discuss that we would fast on Asarah BTevet even on Shabbos, it can never happen!
Minchat Chinuch: The mitzvah to eat on Shabbos and the mitzvah to fast are both מדברי סופרים. If so we should always apply שב ואל תעשה and fast on Shabbos!
If Zechariah is the source for the fasts, the fast for the breaching of the walls was on the 9th of Tammuz, how could Chazal change the date to the 17th?
Shiur provided courtesy of Torah Anytime