Don’t Despair

Little Johnny watched, fascinated, as his mother sprayed furniture polish on her old dining-room table. “Why do you do that, Mommy?” he asked. “To make the table beautiful,” said his mother, who then began removing the foam with a tissue. “What’s the matter?” asked Little Johnny. “Giving up already?”
While the Beis HaMikdash was standing, most locales had the mitzvah of lulav and esrog for only one day of Sukkos, but the mitzvah lasted for seven days in the Beis HaMikdash. Some commentators suggest that the mitzvah was seven days on the entire Temple Mount or even perhaps in all of Yerushalayim. After the Beis HaMikdash was destroyed, Rebbe Yochanan ben Zakai enacted that all locales should fulfill the mitzvah of lulav and esrog for seven days as a remembrance of what was the common practice in the vicinity of the Beis HaMikdash.
The mishnah (Rosh Hashanah 30a) lists another enactment that Rebbe Yochanan ben Zakai made at the same time as the aforementioned one. There is a biblical prohibition against the consumption of grain from the new crop until the Korban Omer was brought on the second day of Pesach. If one was not present at the Beis HaMikdash, he could begin to eat from the new crop of grain at midday on the 16th of Nissan. This is because one can safely assume that the Korban Omer was certainly brought by midday. Once the Beis HaMikdash was destroyed, the new grain is permitted immediately on the morning of the 16th of Nissan (the second day of Pesach). However, Rebbe Yochanan ben Zakai instituted that for the duration of the entire 16th day of Nissan, the new grain should not be consumed.