Tisha Baav is not only a holiday that enables us to reflect on the tragedies of the past but probably more importantly affords us an opportunity to look forward to the blessings of the future. There are actually various laws that are in practice nowadays which operate solely on the principle of "מהרה יבנה המקדש" (“The Temple will be speedily rebuilt”). The underlying principle of מהרה יבנה המקדש functions as follows: Wherever the rebuilding of the בית המקדש would cause a change that would necessitate a greater stringency in the ruling of a certain law, then we must rule more strictly even now when there is no בית המקדש. The fear is that “the Temple will be speedily rebuilt” and people will say, “Last year we were lenient regarding this law,” not realizing that last year’s leniency was only due to the absence of a בית המקדש. For example, רבן יוחנן בן זכאי decreed that it is forbidden to eat from the new grain for the entire day of the 16th of ניסן even though the Halacha is that when there is no בית המקדש (and therefore no קרבן העומר) the new grain becomes permissible at dawn of the 16th of ניסן. This decree was issued for fear thatמהרה יבנה בית המקדש and the people will say “last year (when there was no מקדש, did we not eat from the new grain at dawn?” The people will end up eating from the new grain at dawn when in fact they are required to wait until the עמר sacrifice is offered.
The Talmud in Masechet Taanit 17a mentions a dispute betweenתנאים regarding the application of מהרה יבנה המקדש to the law of שתויי יין (the prohibition of Kohanim taking part in the service when they are under the influence of wine). The חכמים maintain that nowadays Kohanim may not drink wine since the בית המקדש will be speedily rebuilt and a Kohen fit for service will be needed. Rabbi Yehuda Hanasi disagrees and mentions that Kohanim may drink wine explaining שתקנתו קלקלתו i.e. that which disqualifies the Kohen from serving (the destruction of the בית המקדש) permits him to drink wine. Rashi explains that according to Rabbi Yehuda Hanasi since it has been a number of years that the מקדש has not been restored we do not take into account that the מקדש may be rebuilt. Halacha follows Rabbi Yehuda Hanassi (as stated in מסכת תענית) therefore Kohanim may drink wine nowadays. The Gevurot Ari raises the obvious difficulty. Why does the Talmud rule in accordance with Rabbi Yehuda Hanassi’s opinion when in fact, this contradicts the widely accepted principle of מהרה יבנה המקדש?
The answer to this difficulty lies in the basic difference between שתוי יין and the other cases of מהרה יבנה המקדש. In the case of the new grain, for example, the fear is that someone, somewhere will err and eat from the new grain before the קרבן עומר is offered. There is a reasonable likelihood that this error will occur. However, in the case of the Kohanim, the undesired result (of a Kohen performing the service while under the influence of wine) will only occur if there are no other Kohanim fit for service. The possibility that all Kohanim in the world will be שתויי יין on the day the מקדש is rebuilt is highly unlikely. Secondly, it is also highly unlikely that the מקדש be rebuilt with suddenness that the Kohanim would not even have time for the wine to wear off. May we be זוכה this תשעה באב to a true מועד and the fulfillment of מהרה יבנה המקדש.