Rebbe Nachman explains that the true tzaddik is the true beauty and grace of the world. This tzaddik represents the luminaries of light which illumine a person’s mind and path throughout life. Conversely, there are luminaries of fire, which consume a person’s life with false paths and devotions and steer the person away from God. As the Rebbe explains, the tzaddik is the light which illumines the Temple and all that it stands for. Therefore, the Midrash teaches that the passing of the tzaddikim is more severe to our nation than the destruction of the Temple (Eikhah Rabbah 1:37), for when the tzaddik departs, his illumination also departs, and the world is left with the illumination of fire which can be very destructive.
Reb Noson explains further. There are four fasts relating to the Temple: 3 Tishrei, 10 Tevet, 17 Tammuz and Tisha (9) b’Av. These correspond to the four elements (fire, air, water, earth), which are the basic composite makeup of everything in the world. All these four elements are drawn from the tzaddik, who is the comprehensive element containing all the other four elements. Our food, too, contains these four elements. When we eat in holiness, we are drawing our life force from the tzaddik, the comprehensive root of the four elements and we merit to live a balanced life. But fire is an element that, when disconnected from the tzaddik, leads a person into heated conditions—whether hot blood to commit sins, maybe it’s anger, or strife and contention, or any other imbalanced type of lifestyle. His meals are subjected to burning desires which lead him further astray.
Therefore, when the Temple was destroyed, our Sages declared we must fast. We must subdue our four elements, our burning inner desires, and subject them to the ideas and illumination of the tzaddik, the luminary of light. By mourning the Temple, by fasting and crying over its destruction, we merit to rebuild the Temple, to rebuild our lives and minds and know with clarity through an illumined mind what our goals in life should be (based on Likutey Halakhot, Ta’anit 3).