Sound the shofar on the month, when it is hidden for the day of our festival. (Tehillim 81:4)
If on the day of Rosh Hashanah, the moon is hidden from view, why did the verse say that the moon is hidden “for the day of our festival”? The verse should have said that the moon is hidden “on the day of our festival”!
This can be understood from what our Sages of blessed memory said (Beresheet Rabbah 11:2), that after the sixth day of Creation there was no night, but the day continued to shine throughout the Shabbat; that is why there is no verse that says, “and it was evening and it was morning, the seventh day.” Furthermore, Adam Harishon was created on the sixth day, and it is known that that same sixth day was the first Rosh Hashanah in the world. It turns out that from the time the sun rose at dawn on the sixth day, it did not set until the end of Shabbat. This supports the fact that Rosh Hashanah is celebrated on two consecutive days, even in the Land of Israel; and it also supports what our Sages of blessed memory said, that the two days of Rosh Hashanah are one long day.
Now, since on the world’s first Rosh Hashanah the day shone consecutively from Friday to Shabbat night, the moon did not have to be present. That is why the verse said that the moon was hidden “for the day of our festival,” for that Shabbat night that did not happen she was necessarily hidden, because, what light can a “candle” (the moon) give in broad daylight?
We learn that Hakadosh Baruch Hu extended the day in this way on the first Rosh Hashanah because, as is known, light is mercy and darkness is judgment. Hashem wanted to treat His creatures with mercy on the day destined to be of judgment.
That is why the verse says to sound the shofar, because, although the moon already existed in the world, she was intentionally hidden for the day of our festival. She was not necessarily hidden because of her monthly renewal, but rather she was hidden precisely so that the day of judgment on which the shofar is blown would be all mercy and the creatures are favored.
(Zera Shimshon, parashat Vayelech, letter het)
