As I described in detail in my book Mysteries of Judaism, the ancient religious Jewish group Pharisees, who existed from about 320 BCE until 70 CE, and the rabbis who followed them changed all of the Jewish practices and holidays mentioned in the Torah in some ways, without any exception. As a result, Jews are not observing Torah Judaism but Rabbinical Judaism. The law of counting the omer, called in Hebrew Sefirat Ha’Omer, and the holiday of Shavuot are examples.
The counting and Shavuot
Leviticus 23 speaks about the holidays of Passover on the fourteenth day of the first month and the seven day holiday of The Feast of Unleavened Bread that begins on the fifteenth day. In 23:15 and 23:16 the Torah states: “You should count from the day after the Sabbath, from the day that you brought the Omer that is waived [a weight of barley grain]; seven weeks; they should be complete; until the day after the seventh Sabbath, you should count fifty days” [when a new offering is brought in the temple of the newly harvested wheat grain]. The fiftieth day is called Shavuot, or “weeks,” because it concludes the seven weeks from “the Sabbath” mentioned in Leviticus 23:15-16.
The plain sense of this command is that the Israelites should observe the celebration of the wheat harvest on the fiftieth day after the Sabbath following the holiday of Passover. The counting begins on a Sunday and Shavuot is to be observed on a Sunday. In essence, the holiday of Shavuot has no significance in the Bible other than a harvest festival celebrated by the offering of a sacrifice and the number seven, which I will discuss below. The word “Sabbath,” used twice in the command is the seventh day; “they shall be complete [weeks]” is seven days from Sunday through Saturday; and the command to count does not require a verbal counting, just as a verbal counting is not required when the Torah states that a menstruate “must count seven clean [bloodless] days” before becoming clean (Leviticus 15:28) and the Israelites didn’t have to physically “count seven cycles of Sabbatical years” until the Jubilee year (Leviticus 25:8). It is also no surprise that the Bible was unable to set a date when Shavuot would occur since the date of the Sunday when the count began varied from year to year. However, the rabbis created a law requiring Jews to physically count each day, not weeks, between Passover and Shavuot, gave an entirely new significance to Shavuot, and set the sixth day of the month Sivan as the date of Shavuot.
Why seven weeks?
The name of the holiday, Shavuot, means weeks. The number of weeks after Passover until the celebration of the harvest and the offering of a thanksgiving sacrifice to God is seven, why seven?
Seven is an important number in Judaism. The Bible begins with the story of creation, that God created the world in six days and ceased creation (rested) on the seventh. Jews are instructed to observe the seventh day as Shabbat. Among other things, Shabbat reminds the Jew of God, that God created the world, and God gave people certain laws. To emphasize this important lesson, the number seven reoccurs many times in Jewish holidays and practices. I gave examples of well over a hundred usages of the number seven in Judaism in my book Maimonides and the Biblical Prophets.
Among the others, I pointed out that seven is used for days (the Sabbath), months (the holiday of Rosh Hashanah occurs at the outset of the seventh month), years (the seventh year is the Sabbatical Year), Sabbatical Years (the fiftieth year is the Jubilee Year). What is missing in this constant reminder of the basic teaching is weeks. I understand that this was the purpose of celebrating the harvest seven weeks after Passover. And this is why the holiday is called Shavuot, “weeks,” because seven weeks is its purpose, the counting of seven weeks recalls the message of seven, that there is a God who created the world and gave commands.
Changing the biblical command
Why was there a need to change the practice of counting seven weeks to counting forty-nine days and giving Shavuot a new purpose and a new date? The changes were necessary because after the second temple was destroyed and Jews stopped offering sacrifices, the central ceremony of the biblical Shavuot, the offering of the newly harvested wheat grain, could no longer be done. There were now two options. One, cease observing Shavuot. Two, give Shavuot an entirely new meaning, even one not even suggested in the Torah. Jewish ancestors opted for the second choice.
The Torah does not give a date when the Decalogue was revealed on Mount Sinai. Also, as indicated previously, no date was given for Shavuot, only that it occurred on the fiftieth day after the Sabbath following Passover. The new meaning of Shavuot changed the interpretation of the “Sabbath” to mean the first day of Passover, understanding “Sabbath” in these verses as meaning a rest day, not the seventh day of the week. The concept of “weeks,” which gave Shavuot its name, was ignored, and the focus was on the forty-nine days, with Shavuot being on the fiftieth day after the first day of Passover. Since the date of Passover is given in the Torah, the fiftieth day after it could be identified, it being the sixth day of the month Sivan. Six Sivan was given the new interpretation, not mentioned in the Torah, as the date of the revelation of the Decalogue, which was later said to be the date of the giving of the Torah, even though it is clear from the Torah itself that the Torah narrates events that occurred after Sinai.
The physical practice of counting the “days of the omer” instead of thinking about the seven weeks, was also instituted to heighten the significance of the Torah. Each day, for forty-nine days, Jews were encouraged to count the days of the omer, thereby reminding them each day that the holiday of Shavuot is approaching, commemorating the most significant day in Jewish history, the day God revealed the Torah.
The omer blessing
Since the counting of the days of the omer is not a biblical commandment, why did the rabbis institute the practice of saying a blessing each night before the count in which the Jew states that God gave the command? “Blessed are you Lord our God, king of the universe, who made us holy through His commandments, and commanded us concerning the counting of the omer.”
There are at least two answers. The prayer does not say “counting the days of the omer. The duty to count the weeks of the omer, is in the Torah. Thus, arguably, God commanded the counting.
Second, the rabbis insisted that the Torah mandated that Jews follow the rabbinical interpretations of the Torah, so, by counting days, Jews are observing the divine decree. The rabbis derived their authority from Deuteronomy 17:8-13 which states that when future judges, which the rabbis said includes them, tell you how to act, “According to the law which they will teach you, and according to the judgment they will tell you, you must do. You should not turn aside from the sentence which they will declare to you, neither to the right hand nor to the left.”
Thus, when the rabbis and Pharisees developed new laws, such as the lighting of candles before the Shabbat and this new law of counting days, they told Jews to say a blessing in which the Jews blessed God for making the requirement.
 This essay is an expanded version of what appears in Mysteries of Judaism about the omer.