Chapter 121:3 and 4
Laws of Public Fast Days
3. [Another public fast day] is the tenth of Teves, the day Nebuchadnezzar
(King of Babylon) camped around Jerusalem and began its siege. Ultimately,
this led to the destruction of the first Beit Hamikdash (Temple).
4. The seventeenth of Tammuz [is also a public fast day]; five catastrophes
happened on this date:
a) The tablets [of the Law] were broken (1) when Moses descended from Mount
[Sinai], as related in the Torah [Exodus 32:19].
b) The "Korban Tomid" ("daily sacrifice") ceased to be offered [in the
first Beit Hamikdash, as a result of the siege by Nebuchadnezzar's army].
c) [The walls surrounding] the city of Jerusalem were breached before the
destruction of the Second Temple. Before the destruction of the First
Temple, [the walls] were breached on the ninth of the month, as [Jeremiah
52:6-7] states: "In the fourth month, on the ninth of the month, the famine
became very severe...and the city was breached." However, before the
destruction of the Second Temple, [the walls] were breached on the
seventeenth of the month, and that day became a public fast, as opposed to
the ninth, because] the destruction of the Second Temple affected us more
severely (2). .
(Furthermore, the Jerusalem Talmud relates that, before the destruction of
the First Temple as well, it was on the seventeenth of Tammuz that the
city's walls were destroyed)
d) The wicked general, Apostumus, burned a Torah scroll.
e) An idol was set up in the Temple Sanctuary by a group of evil
Jews. This led to the Temple's destruction and our exile.
(1) That is, the two stone tablets ("luchos") upon which the Ten
Commandments were written; when Moses descended from Mt Sinai, and saw the
Jews dancing around the Golden Calf, he shattered the Tablets on the ground.
(2) In the sense that we are still suffering in the exile created by the
destruction of the second Beit Hamikdash.