Daf Yomi - Rosh Hashana 30 - Descending from Heaven

Rabban Yochanan ben Zakai instituted that one is not permitted to eat from the new grain the entire day of the sixteenth of Nissan. In the times of the Bais HaMikdash, the new grain could only be eaten after the omer offering was brought on the sixteenth of Nissan. Subsequent to the destruction of the Bais HaMikdash, one was biblically permitted to eat the new grain on the sixteenth of Nissan in the morning. Rabban Yochanan Ben Zakkai was concerned, however, that the Bais HaMikdash may be built the following year on the night of the sixteenth of Nissan and there would not be enough time to prepare the omer offering. People might then say that the new grain will be permitted in the morning just as it was the previous year. This assumption would be erroneous, because the previous year there was no Bais HaMikdash, thus there was no possibility of offering the omer, and for that reason the new grain was permitted in the morning. During the present year, however, there is a Bais HaMikdash and one must wait for the offering of the omer or one must wait until the end of the day. Rabban Yochanan Ben Zakkai therefore instituted that one was prohibited from eating the new grain the entire day of the sixteenth of Nissan.

Rashi wonders how the Bais HaMikdash could be built on the night of the sixteenth of Nissan, as the Gemara in Shevuos 15b states that the Bais HaMikdash cannot be built at night. Rashi answers that it is only regarding a Bais HaMikdash built by humans that there is a restriction of building it at night. The third Bais HaMikdash, however, will descend from Heaven miraculously, thus there are no restrictions regarding the building of the third Bais HaMikdash.

The Maharil Diskin is troubled by this answer, as the Jewish People have an obligation to build the Bais HaMikdash, so why would HaShem prevent us from performing this mitzvah?

The Maharil Diskin answers based on a Medrash in Eicha that states that when the Bais HaMikdash was destroyed, the gates of the Bais HaMikdash sank into the ground and in the future, the Jewish People will excavate the gates and affix them to the Bais HaMikdash. The Gemara in Bava Basra rules that one who secures the gates in an ownerless field is deemed to be the one who acquires the field. Thus, we will fulfill the mitzvah of building the Bais HaMikdash when we secure the gates of the Bais HaMikdash. This can also be the explanation of the words that we recite in the Shemone Esrei of Mussaf on the festivals, show us its rebuilding and gladden us in its perfection. The word for perfection is tikkuno, which can allude to the securing of the Bais HaMikdash gates.