On the ninth day of Av, the anniversary of the destruction of the Temple, when the Jews mourn the long years of their exile, the congregants sit upon the floors of their synagogues to chant the traditional Lamentations, and the one who leads the prayers declares, "So-and-so many years have passed since the destruction of the Temple."
For the grief of banishment and dispersion is identical with, and emerges from, the grief at the destruction of the Holy City and the Temple.
At the same time, the mourning for the ruin of Jerusalem is far deeper and more personal than would appear from its public nature.
It betokens more than the loss of the most sacred of the holy places or of the national capital.
It is a blow to the very existence of the people.
Indeed, the whole world feels the hurt, and according to tradition, it will not return to primal perfection until the city is rebuilt.
For Jerusalem is indispensable to the well-being of the world.
–Rabbi Adin Steinsaltz
From “Remembering Jerusalem,” in The Strife of the Spirit by Rabbi Adin Steinsaltz