The parsha of Devarim is always read in the beginning of the Hebrew month of Av, just before the ninth of Av, when we commemorate the destruction of the two Temples.  The parsha of Devarim opens with severe, but hidden reproaches of Israel transmitted by Moshe.  The purpose of these reproaches is obviously to encourage teshuvah-repentance.

The "three weeks," which begin with the fast of the seventeenth of Tammuz and finish with the fast of the ninth of Av, are called the weeks of "Bayn hametzarim," the time between the troubles.  On the seventeenth of Tammuz, the walls of Yerushalayim were breached and the enemy entered into the city.  On the ninth of Av, the destruction of the Temple completed the calamities.

Also, this name, "Bayn hametzarim," implies that, during this time, we are in a state of constriction, pressured on all sides into narrow subsistence, and the expansiveness of the good life is completely forgotten, because of the troubles which afflicted us during this period. Those who find the intimation of things have also construed the letters which spell the name of the month of Tammuz, when the three week period begins, to mean "zemanay teshuvah memamashim uba'im": i.e., the time of teshuvah is approaching and coming into effect. These intimations were made for a serious purpose: to emphasize the connection between the past and the future. 

Teshuva-repentance, which literally means "return," erases the past, when a person returns to the source of things and accepts its guidelines for the future.  The calamities of the past promote in a person the feelings of regret, pain and sorrow for the sins, which caused them.Through teshuvah the sin itself becomes a vehicle, which encourages a person to come close to G-d and serve Him.  This is the simple meaning of the saying of the sages that ‘where those who have done teshuvah stand, perfect tzadikim cannot stand.’ 

And Chazal has used a similar logic, when they said that anyone who mourns over Yerushalayim merits seeing her consolation.  In other words, the pain of the destruction is one of the building blocks of the future construction and redemption. Nevertheless, in order to understand how mourning for the past becomes the foundation for the future Redemption, we must examine more deeply the question of what mourning is? Mourning is a conscious realization and heartfelt contemplation upon the emptiness of material existence! Most normal people feel frightened, when they are confronted by a dead body or by death in general.

A person is so frightened by the inevitability of his own death that he normally manages to exclude it from his consciousness altogether.  In his heart, he thinks, "This won't happen to me." A person is so strongly attached to the material plane of existence that he identifies himself entirely with life in this world.  To even think about the inevitable moment when he will become separated from this powerful identification with material existence is, in effect, to nullify his own personal ego identity; and there is nothing more frightening to a person than the nullification of his ego identity. On the other hand, the greater a person is, the more is he aware that his true identity is his soul, which is eternal and indestructible.