Many of the prohibitions and customs relating to the day of Tisha B’av are the same that relate to a mourner. For example, we sit on the floor and refrain from greeting people. Why then do we not tear kriyah, one of the most fundamental signs of intense mourning, on Tisha B’av?
One possible answer is that Kriyah is too intense a form of mourning. Soon after the destruction of the Second Temple the sages sought to establish a uniform set of rules for mourning the destruction. Some sages felt that eating meat and drinking wine should be completely forbidden. The majority of the sages, however, felt that completely prohibiting meat and wine would simply be too intense and would plunge the Jewish People into a state of constant mourning and depression. These sages understood that life must go on, so they confined the intense mourning period in which meat and wine are in fact prohibited to the week directly preceding the fast of Tisha B’av. Tearing kriyah is such an intense physical act of mourning that the sages did not want it performed on Tisha B’av for fear that the sight of the torn garment would cause a feeling of despair and depression that would be impossible to overcome. Although the first half of Tisha B’av is solely concerned with mourning and sadness the second part of the day is focused on supplication, repentance, and hope.
Another answer that I heard from a student of mine is as follows. There is a fundamental difference between the mourning for a person and the mourning over the destruction. A person is helpless when faced with the death of a loved one. Man cannot control death. Man can only react to it, and he does so by tearing his garment as a sign of total frustration and helplessness. The destruction of the Temple was caused by Man’s sins and therefore, the Talmud teaches, that Man has the ability to rebuild the Temple by repenting for those sins. Since the Second Temple was destroyed because of the sin of “Sinat Chinam – Baseless Hatred”, Man can repent and rebuild the Temple by loving and caring for his fellow Man. Therefore, unlike the frustration that causes the tearing after someone dies, the sorrow caused by the destruction is not irreversible. Man has the power to take control of his actions and change them in a way that will allow the rebuilding of the Temple. Kriyah – Tearing is not required on Tisha B’av, for it is a day that requires just the opposite; mending. When we are able to unite as one harmonious and loving family we will surely see the rebuilding of the Temple, may it happen very soon.