[based on a dvar torah given by Rabbi Aryeh Lebowitz]

There is a mnemonic that Chazal created to help us remember when we read certain parshios throughout the year. The mnemonic as quoted in Shulchan Aruch, Orach Chaim, Siman 428:
פקדו ופסחו, ולמעוברת סגרו ופסחו, מנו ועצרו, צומו וצלו, קומו ותקעו

Question 2: Moshe says in Devarim 1:37 that Hashem punished him, by not allowing him to enter Eretz Yisrael, because of Bnei Yisrael’s sin of the Meraglim:
גַּם בִּי הִתְאַנַּף ה’ בִּגְלַלְכֶם לֵאמֹר גַּם אַתָּה לֹא תָבֹא שָׁם

Why is Moshe blaming Bnei Yisrael for being denied entry to the Land; wasn’t he punished because he hit the rock, instead of speaking to it?

Question 3: The Midrash in Meggilas Eicha instructs us to read Devarim 1:12 in the somber tune of Meggilas Eicha. The passuk begins with the word “eicha,” and in it Moshe recounts his feelings that he could no longer bear the burden of the multitude of the people. Other than the word “eichah”, what link is there between this passuk/Parshas Devarim, and 9Av?

To begin, there is certainly a link between Devarim and 9Av: As Rashi explains at the beginning of Devarim, Moshe lists all the places where Bnei Yisrael traveled where something bad happened, to hint to them that they should remember their missteps in that location. Since 9Av is a result of our sins, it is fitting to hear Moshe’s mussar, with regards to our sins, on the Shabbat before 9Av.

Rav Soloveitchik points out further, that the only sin that Moshe expounds upon in detail and explicitly states in the parsha, is Cheit HaMeraglim – the sin occurred on 9Av ,and triggered all future suffering on this day. To understand this, we must recognize the degreeof devestation of the Meraglim. Before the Meraglim, Bnei Yisrael were on a tremendous high, making their way out of slavery, with the Torah in hand, on the way to the Promised Land. Along comes the damaging report of the Meraglim, and Bnei Yisrael plummet drastically. The ultimate and final gift after all Bnei Yisrael endured, and after all miracles Hashem performed, was Eretz Yisrael…and we spit, kaviyachol, in Hashem’s face, by believing the spies’ negative report. 

Cheit HaMeraglim is the culmination of all of Bnei Yisrael’s complaining and all the jabs they took at Moshe by asking ‘why did YOU [Moshe] take us out of Egypt to die in the desert’. It was a lack of emunah that was too much to recover from, and why that generation dies in the desert. Moshe knew it wasn’t him that really took Bnei Yisrael out and was testing them, but after a while it had a tiny effect on him. It is this frustration that causes him to veer ever so slightly from Hashem’s word at Mei Meriva. Moshe hits the rock because he reaches a breaking point precipitated by Cheit HaMeraglim. 

As noted, Cheit HaMeraglim was the first of the major catastrophes to happen on 9Av. According to Megilla 31b, some Tanaaim held that we should read the story of the Meraglim in Parshas Shlach on the morning of 9Av. We, however, follow a different opinion and read from Va’eschanan…
A shift occurred where we went from using 9Av only as a day to remember the bad things in Parshas Devarim, to a day where we also think to the future and pray. 
“Fast and pray,” say Chazal; make sure you pray after you fast. We certainly mourn all the terrible things that happened, but we don’t wallow and abandone hope. We don’t mourn just to mourn, so we can say, ‘woe unto us’. The reason for the fasting is for us feel our distance from Hashem, and use that aching feeling to move closer toward Him. If fasting doesn’t motivate us to pray to move closer to Hashem, then it didn’t fulfill it’s purpose.
The goal is “V’shavta ad Hashem elokecha v’shamata b’kolo”