Zechariah #11 (Chapters 7-8)
In Kislev of the fourth year of Darius (two years into the building of Bayit Sheni but before its completion) a delegation from Bavel asked if they still needed to fast for the destruction of the first Beit HaMikdash. Why did they not ask about the other fasts, only Tisha B'Av? Malbim: They wanted to know if the new Beit HaMikdash being built will be as great as the first (in which case there was no reason to fast) because of the seven items absent from the second Beit HaMikdash that were present in the first.
God's answer is that they are asking the wrong question, it's not about the fasting, it's about the goal of fasting.
Delivered at the OU Israel Center, June 24th, 2019, 21 Sivan 5779