Parshas Devorim is always read the Shabbos before Tisha B'Av. Many think it is because of the posuk "eicha esa l'vadi" which is read in the tune of Eicha. But there is also an important conceptual connection between the parsha and Tisha B'Av.
In his rebuke of Bnei Yisrael, Moshe Rabbeinu focuses much of his attention on the sin of the spies. At first glance, the sin of the spies lay in the fact that the spies and the people refused to trust that Hashem would be able to keep his promise to take them into Eretz Yisrael and defeat the nations living there. But in this week's parsha the Torah adds another dimension to the story. In describing how the people asked him to send spies, Moshe says, "Va'tikrivun eilay kulchem - and all of you approached me." Rashi comments, "kulchem, b'irbuviyah" - the word kulchem implies they came as a mixed-up, confused throng of people. They didn't come in an organized fashion, with the leaders in front, followed by the elders, and then the younger people. Rather, everyone came together, as one mass, with each one pushing the other.
Rav Yeruchem Levovitz zt"l explains that this demonstrated that the people felt under pressure. They felt a sense of urgency to send the spies, and they couldn't contain themselves, so they lost their composure. They didn't act with patience; they didn't present their case in a deliberate and measured way; they pushed.
This highlighted an even bigger problem - the people felt that they had to take charge. It was up to them to prepare for the battles ahead, to take control of their situation. To be sure, this approach was not completely mistaken. After all, Bnei Yisrael left Mitzrayim with weapons (see Rashi, Shemos 13:18). In sefer Yehoshua, Bnei Yisrael fought many battles against the nations living in Eretz Yisrael. It's not as if Hashem wanted the people to sit back and let Him do all the work miraculously. Once Bnei Yisrael left the desert, they were expected to engage in hishtadlus, so that their success would come b'derech ha'teva. This is very much a part of a Torah way of life.
But the question is: who is running the show? Is it my intelligence, my insight, my effort, that enables me to accomplish? Or are my efforts just a vehicle to enable Hashem to bring me success? The difference is subtle, but critical. This was the underlying mistake of Bnei Yisrael. It wasn't the fact that they sent spies; it was the way they went about sending the spies. They lost perspective. They got carried away with themselves. They forgot that Hashem is the One who is really in control. They felt anxious and under pressure. So they pushed their way to Moshe to demand action.
"You cried an unnecessary cry; so I will establish a cry for generations" (Ta'anis 29a). Chazal tell us that the destruction of the Beis HaMikdash on Tisha B'Av was a response to the crying of Bnei Yisrael upon hearing the report of the spies. The loss of the Beis HaMikdash is not just a punishment for the sin of the spies, but is also the result of the same improper perspective that led to the sin in the first place. Since one of the middos of Hakadosh Boruch Hu is emes, and the Beis HaMikdash is the primary dwelling of the Shechina in this world, the Beis HaMikdash should naturally be a place where a person achieves absolute clarity in his perspective on life. In the shadow of the Beis HaMikdash all selfish motivations should disappear. A person should appreciate that "life is not about me," and he should accept to serve Hashem as fully as possible.
And yet, during the first Beis HaMikdash, Klal Yisrael engaged in murder and immorality, both of which stem from a self-centered attitude. They served avodah zarah even in the Beis HaMikdash itself. What greater act of hubris against Hashem can there be! The second Beis HaMikdash was destroyed because of sinas chinam - baseless hatred (Yoma 9b). The Vilna Gaon writes (Even Shleimah 3:2) that the cause of sinas chinam is a lack of bitachon in Hakadosh Boruch Hu. A person who believes that he has to get ahead of others in order to succeed in life will naturally feel jealousy and hatred toward those he perceives as his competitors.
When Klal Yisrael fails to appreciate the gift of the Beis HaMikdash and engages in behavior that runs counter to everything the Beis HaMikdash stands for, if we get too wrapped up in ourselves and we forget the lesson of the spies, then Hakadosh Boruch Hu has no choice but to remove the Beis HaMikdash, to take extreme measures to help us regain the proper perspective.
May the day of Tisha B'Av give us the clarity of vision to serve Hashem properly, and in that merit may we see the rebuilding of the Beis HaMikdash speedily in our days.