While according to the opinion that Moshe’s priesthood was everlasting it is understood why he is taken into account when determining the amount of water that is to be in the kiyor, according to the opinion that he was a priest for a mere seven days, this is not understood.
If Moshe only served as a kohen during the inauguration of the Tabernacle—indicating that from then on, the kiyor was only needed for Aharon and his sons—why then, for all eternity must the kiyor have enough water for four kohanim? Why should Moshe be enumerated as one of the kohanim if he only served as such for the seven days of the inauguration of the Mishkan?
Explanation
The days of inauguration were a preparation for the general service in the Mishkan afterwards. Being that the entire existence of the kiyor served as a preparation for its general service, its measurements therefore included that which was also needed only during the time of the inauguration of the Mishkan.
While Moshe was only considered a kohen during the days of preparation, the entire idea of the kiyor was indicative of preparation. Moshe’s need for its use during this stage was thus included in the measurements of its permanent dimensions.
This idea leads to an interesting conclusion: although the kiyor merely served as a preparation for the service in the Mishkan, and thus in many ways, retained a lower level of holiness, it simultaneously possessed an aspect that was greater than the rest of the vessels.
It was for this reason that the kiyor contained an aspect that alluded to Moshe, who was greater than his brother Aharon.
Thus, although in a general sense the kiyor was lower than the rest of the vessels, it also held a unique superior quality from all the other vessels in the Tabernacle.
Two extremes
These two extremes found in the kiyor in which, on one hand, it only held the status of a preparatory vessel and on the other, it contained the superior quality of Moshe being expressed therein, are also expressed in the specific material from which it was made.
The Torah says as follows:
Text 9
You shall make a washstand of copper and its base of copper for washing, and you shall place it between the Tent of Meeting and the altar, and you shall put water therein.
Shemos, 30:18
The Torah relates that the specific copper that was used for the construction of the kiyor was from copper mirrors that were donated by the Jewish women.
