The way our calendar is set up, parshas Vaeschanan is always Shabbos Nachamu, when we read the first Haftora of consoling, Nachamu Nachamu Ami, console console My nation. It is also the Shabbos right before or after Tu B'Av, and sometimes it falls on this Shabbos itself. Tu B'Av is the 15th of Av, of which the Mishnah tells us, "There weren't holidays for Israel, like the 15th of Av and Yom Kippur." In other words, the holidays of Tu B'Av and Yom Kippur are ranked as the greatest holidays we have.
What is the connection between parshas Vaeschanan, Nachamu Nachamu and Tu B'Av? Why is Tu B'Av so great?
From the words of the Mishnah, it seems that Tu B'Av is even greater than Pesach, Shavuoth and Sukkos. Why is Tu B'Av so great?
The Pri Eitz Chaim, which is a work on Kabballa, says that it is because at that time the moon is full. But aren't Pesach and Sukkos also on the 15th of the month, when the moon is full? So what makes Tu B'Av greater than Pesach and Sukkos?
The answer that is given to this question, is that because Tu B'Av comes in contrast to Tisha B'Av and the Three Weeks, the saddest time on the Jewish calendar when our Temples were destroyed and we were thrown into exile, therefore it is the greatest holiday.
You may ask, doesn't Pesach also come in contrast to the exile in Egypt? What makes Tu B'Av greater than Pesach?
The exile in Egypt was before we received the Torah. When we received the Torah, we became a "Kingdom of Kohanim and a holy nation." When we went into exile after the destruction of the Temple, it was the exile of a Kingdom of Kohanim and a holy nation, which is a more painful exile than the Egyptian exile, in which we were just a nation.
Tu B'Av represents the opposite of Tisha B'Av. Tisha B'Av we went into exile because of our sins. As we read in the Yom Tov Mussaf prayer, "Because of our sins we were exiled from our land." Tu B'Av, on the other hand, is a time of forgiveness of sin, that's why the Mishnah mentions it together with Yom Kippur, which is also a time of forgiveness of sin. Tu B'Av represents what is accomplished through our descent into exile, the coming of Moshiach and everlasting life. For the greater the descent, the greater is the ascent that follows. It is our efforts in this dark and bitter exile, that accomplishes the coming of Moshiach, which is everlasting, and the building of the Third Temple, that will be everlasting.
The Mishnah continues to say, that on Yom Kippur and on Tu B'Av, the daughters of Jerusalem (or Israel) would go out to the vineyards and dance. What moved them to dance specifically on those two days? The daughters of Israel sensed Hashem's joy, forgiving us, that filled them with joy, and so they danced.
Vaeschanan means and I prayed. Moshe prayed that he should lead the Jewish people into the land of Israel. The reason that he wanted to lead them into the land, was because everything that Moshe did was everlasting. He knew that if he would lead the Jewish people into Israel and build the Temple, it would be everlasting and no exile would follow. In other words, Moshiach would come.
When it says Nachamu Nachamu, it is referring to us being consoled when Moshiach comes. The double expression of Nachamu, doesn't mean just two, rather it means multiple, everlasting, that we will be consoled forever.
Now we see how Vaeschanan, Nachamu and Tu B'Av are connected. They are about the coming of Moshiach and everlasting life. Now that we have descended to the lowest possible place in the exile, and accomplished our mission, it is time for Moshiach to come and lead us to the greatest and everlasting ascent. May it happen soon, the time has come.