The legend that on the day of Tisha b'Av, at the very time of the Destruction of the Temple, the Messiah was born, is a key to the understanding of one aspect of the problem of the destruction and the notion of redemption.
For redemption to take place, the repair of the various individual destructions alone is insufficient.
Even if all people of Israel were to return to their land, this would be insufficient for the redemption of the Destruction.
Furthermore, even the building of the Temple in and of itself could not repair that which had been damaged in the course of the generations.
Only the Messiah, who will bring redemption to the world on a higher plane and in a more complete fashion than ever before possible, can undo the Destruction.
Redemption cannot simply be a return to the situation as it previously existed; it must be much more than that, a higher stage.
The reestablishment of a Jewish state, in the sense that it is merely a restoration, is therefore only a small part of the scheme of redemption.
It is only true redemption that can reconstruct the Jewish people, not only as it formerly existed but on an even higher plane.
The redemption of the Jewish people cannot be complete until it is accomplished by a change in the entire world.
Only a redemption that rises above the sufferings of two thousand years, which leads from them to a higher level of existence, can be considered full reparation for the Destruction.
–Rabbi Adin Steinsaltz
From The Long Shorter Way by Rabbi Adin Steinsaltz