These are the feasts of G-d. the holy convocations, which you shall proclaim in their seasons (Lev. 23:2)
In the days of the Holy Temple, the calendar was fixed and the determination of when the festivals would fall was done by the Sanhedrin, according to the testimony of witnesses who said they had seen the new moon. Even if after the fact, it was discovered that a mistake had been made, the court's decision was final and the holiday celebrated according to their calculations. G-d gave man the absolute power to determine when a festival fell and to imbue the day with holiness.
And you shall take...willows of the brook (Lev. 23:40)
The willow, one of the four kinds we take on the holiday of Sukkot, has neither fragrance nor taste. It symbolizes those Jews who have in their possession neither Torah learning nor good deeds. Their only merit is the fact that they are descendants of Abraham, Isaac and Jacob.
Maimonides teaches that even a willow that did not grow on the banks of a brook, say, one that was found growing in a desert or on a mountain-top, is kosher and may be used to perform the mitzva. Likewise, a Jew who did not grow up close to his roots in Judaism and was raised in a foreign culture, through no fault of his own, is also kosher, just by virtue of his being a Jew. (Lubavitcher Rebbe, shlita)
Seven complete weeks shall there be (Lev. 23:15)
The Jewish People is likened to a seven-branched menora, each branch of which symbolizes a different approach to the worship of G-d. There are Jews whose main emphasis in worship is fear of G-d, and others whose love of G-d is the main driving force behind their relationship with the Creator. In all, there are seven different paths to G-dliness. On each day of the omer, a different attribute is stressed and a different path to G-d is purified. These seven attributes can be combined with each other for a total of 49 possible combinations. Just as each day is necessary for the completion of the omer, so too is every individual Jew an integral component of the Jewish People.
