The illustrious Rabbi Levi Yitzchak of Berditchev explains that the day is so named because on this Shabbos, "every Jew is shown from afar a vision of the future Beis HaMikdash."[1]

Of course, the simple reason for the name Shabbos Chazon is that, as the Shabbos closest to the fast of the Ninth of Av, we then read the Haftorah which begins with the words "Chazon Yeshayahu," the "Vision of Yeshayahu" - the last of the three "Haftorahs of Calamity" dealing with the destruction of the Holy Temples and the subsequent Jewish exiles.

Understandably, the closer this Shabbos falls to the Ninth of Av, the greater the calamity; when it immediately precedes the Ninth of Av, or actually falls on the Ninth of Av (with the fast being pushed off to the next day), then calamity is extant to an even greater degree.

Of course, the converse is also true: The vision of the future Beis HaMikdash shown to us on Shabbos Chazon because of its proximity to the fast of the Ninth of Av, is revealed to an even greater extent when the Ninth of Av actually falls on a Shabbos (as is the case this year).

What is the reason for this vision of the future Beis HaMikdash?

Rabbi Levi Yitzchak of Berditchev explains this[2] with the parable of a father who had a precious garment sewn for his son. The boy promptly tore it to shreds. The father then made him a second garment, but the child tore this one up as well. Thereafter, the father had yet another garment sewn for his son. This time, however, he did not permit the lad to wear it. He only let him to gaze upon it at appointed times, telling him that when he chose to conduct himself properly he would be allowed to wear it.

In this way, the father trained his son to act in a manner that ultimately became second nature. At this point, the father gave him the garment and allowed him to wear it.

All Torah parables, as part of the "Torah of Truth," are exact in all their details.[3] This must surely be so regarding a parable offered by the holy rabbi of Berditchev.

Accordingly, we must understand why Rabbi Levi Yitzchak likens the two Holy Temples to two garments, when the nature of a garment is temporary, while the innate quality of the two Holy Temples - were it not for the iniquities of the Jewish people - was that of permanence. Especially so, since the parable could have been drawn using abodes instead of garments.

We must conclude that, notwithstanding the impermanent nature of a garment, it contains a quality that a house lacks. It is for this reason that it is better to liken the Beis HaMikdash to a garment than to a dwelling.

A garment closely follows the proportions of its wearer, while a house is much larger than its inhabitant. The relationship of a garment to its wearer is thus much more precise than that of a house to its inhabitant. Therefore, one can tell much more about a person's physical attributes by his clothing than by his house, which tells us only whether the owner is rich or poor, etc.

This is why the parable refers to garments rather than houses: The Beis HaMikdash incorporated differing degrees of holiness: the Courtyard, the Holy, the Holy of Holies, etc. This is similar to various garments, each of which conforms to the dimensions of its wearer.

This also holds true with regard to the spiritual service of a child and his training not to tear the garments he is given. In the analog, this means that not only does a person devote himself to G-d in a general sense, but also that all the particular aspects of a Jew become so attuned to G-d's will that he becomes incapable of ruining the "garment" he is given.

The child then receives the third garment - the third Beis HaMikdash - not merely in a vision on Shabbos Chazon, but in reality and forever.

Notes: 

1. Quoted in Or HaTorah LaNach, Vol. II, fn. to p. 1097. 

2. Ibid. 

3. See Likkutei Sichos, Vol. I, p.118; Vol. XI, p. 259ff.; Vol. XIX, p. 287.