This Shabbat, the Sabbath before Tisha B'Av, is called Shabbat Chazon. Rabbi Levi Yitzchak of Berditchev used to note that the name comes from the word machaze, meaning "vision," for "on that day everyone is shown the future Holy Temple."
The purpose of this vision is to inspire and encourage a Jew: having caught a glimpse of the Third Holy Temple in its heavenly perfection, all that is left for him to do is to bring it down to this world.
Although not everyone actually sees the Third Holy Temple, everyone is intrinsically affected by it. This is similar to the following episode from the Book of Daniel: "And I Daniel alone saw the vision; the men who were with me did not see the vision, but a great trembling fell upon them..."
Our Sages ask why a dread fell upon the men with Daniel if they had not actually witnessed the vision. They answer: "Though they did not see it, their heavenly soul saw it."
In the same way, on Shabbat Chazon, the soul sees the future Sanctuary; moreover, this perception leaves an impression on the individual, even on his body.
Tuesday, Tisha B'Av, is a fast day. On that day we mourn the destruction of the First and Second Holy Temples and other devastating events that took place on that date.
The Rebbe spoke about the comment of our Sages that Tisha B'Av is the birthday of Moshiach. The Rebbe explained that this is true because the moment the destruction began, the potential for the Redemption also began. And, since Moshiach was "born" on Tisha B'Av, his mazal is stronger and shines brighter on that day.
May we celebrate in actuality the birthday of Moshiach this Tisha B'Av at which time we will be reunited with the Rebbe who will lead us all together to the Complete and Final Redemption.