Deuteronomy is the last book of the Torah and is one long farewell speech from Moshe.
To kick off his speech, Moshe reminds the people of the sin of the spies. The day that the spies brought back the terrifying report is said to be Tisha B’Av, also called the 9th of Av. Throughout history, many terrible things have befallen the Jewish people on this date, and it is now the saddest day on the Jewish calendar.
These events are not easy to understand, but the book of Deuteronomy reiterates that God is the ultimate decision-maker, and His plan is good.
Shabbat Shalom!