The gemara (Taanis 29a) states that upon hearing the report of the spies concerning Eretz Yisroel, the Jewish people cried.  That night was Tisha B’av.  Hakadosh Baruch Hu said, “You cried for no reason, I will give you a reason to cry for all generations.”  Every year, we cry on Tisha b’Av for the two Batei Mikdash that were destroyed on this day.  

If the Churban came about because we cried for no reason, we could derive from this that the Beis HaMikdash will be rebuilt when we recognize that there is no reason to cry.  When something disappointing happens, yet we believe that it is from Hashem, for the good, this awareness will rebuild the Beis HaMikdash. 

~ R’ Elimelech Biderman