For the source text click/tap here: Rosh Hashanah 21
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When the Temple stood, it was essential for the kohanim in the Mikdash to know whether the new month began on the 30th day or the 31st day after the previous Rosh Chodesh, so that they would know when they had to bring the special Mussaf sacrifice for Rosh Chodesh. This was so important that the Sages taught that it would be permissible for witnesses who saw the new moon to travel to the Temple to testify even if it was Shabbat and their travel would involve chillul Shabbat.
After the destruction of the Temple, Rabban Yochanan ben Zakkai ruled that this chillul Shabbat should only be limited to situations when it served an essential purpose.
Without the Temple sacrifices, it was deemed essential only for the months of Nissan and Tishrei, when it was necessary to establish the date of the holidays of Pesach, Yom Kippur and Sukkot.In the next Mishnah we are told of The rabbis go on to discuss Kohelet, King Solomon, who strived to be like Moses. He was the leader who decided that two witnesses were required to put someone to death. One witness was not enough to justify such a severe punishment.
Leaders must be lonely. They are surrounded by people who want to keep them happy. To find role models, they have to look to those who have been successful leaders in the past. Moses is the consummate leader; an obvious choice for King Solomon. But how would a king decide how to adapt that leadership model to his own reign? If Moses was not allowed to have the wisdom of G-d "the fiftieth gate", how should King Solomon use that information to become a better leader?
Just like Moses did not have this (50th Gate of ) wisdom of G-d, neither could one witness have reliable enough information to justify someone's death.
We explore this idea of the 50th gate of wisdom and its Kabbalistic intonations.