Presence

In his introduction to Eicha, R. Gottlieb excerpted a passage from The Lord is Righteous in All His Ways, by R. Soloveitchik (R. JJ Schacter, editor):

If you should ask me what kind of fast day is Tisha B'Av, I would answer that it is the fast day caused by the sin of the spies. The [destruction of the Temple] is only a consequence, a result, of that event. What actually happened was that [God] had to change His plans. Instaed of taking the [Children of Israel] directly into [the Land of Israel] from [Egypt], He kept them in the desret for thirty-eight years, years of agnoy and death and confusion. This was exactly what was responsible later for the destruction of the first [Temple], the second [Temple], Beitar, and all of the catastrophic events that later transpired on Tisha B'Av. This event was the first tragedy associated with Tisha B'Av, and it precipitated the great, awesome tragedy of thousands of years later, the destruction of the [Temple] and the exile.

Assuming we understand the sin of the spies as we have discussed before, as a recapitulation of the primal rejection of Divine authority by Adam, which results in an exile from the Divine Presence, we have a very nice narrative arc. The Children of Israel, descendants of those that first accepted the imperative of Divine authority, redeemed from the throes of slavery, ushered into His Presence and given His Law, now about to enter the Land reserved for the subjects of the King. But suddenly they reject His qualitative assurances in favor of their own estimations, throwing off the yoke of His sovereignty, causing once again an exile from His Presence. But also, setting the stage for generations to come; abide by His authority, or be cast out.

The sin of the spies, the nature of Tisha B'Av, goes back to the very dawn of mankind, stems from our primal instinct to claim power for our own. It seems in our nature to forever repeat this process.