Rosh Hashanah is not a biblical holiday
The following is from my book “Mysteries of Judaism,” in which I point out that Judaism today is Rabbinical Judaism, not Biblical Judaism. I emphasize there that I am an observant Orthodox Jew, and the fact that the ancients changed what is in the Bible does not affect my observance.
The New Year That Wasn’t a New Year
Rosh Hashanah is not a biblical holiday, although it replaced a biblical one, and is notably different from the holiday it replaced. The biblical holiday, Yom Teruah, had a totally different purpose than Rosh Hashanah, which focuses on the onset of a new year, repentance, and commitment to live the next year properly. Yom Teruah concentrated on months and the number seven.
The only mention of rosh hashanah, new year, in the Bible is in the writing of the sixth century BCE prophet Ezekiel. However, Ezekiel was speaking about the first day of the first month later in the post-biblical period, called Nisan. He was not talking about the first day of the seventh month, later called Tishrei, the date of the current holiday of Rosh Hashanah.
According to the Torah and as recognized by the prophet, the beginning of the year is the month later called Nisan. This is the month in which the Israelites who were freed from Egyptian slavery became a nation. The new year is celebrated by Passover and Hag Hamatzot, and the year begins, as does nature, in the spring. It was only during the Babylonian exile of 586 BCE that the Judeans accepted the Babylonian concept that the year begins in the fall, and the first day of the seventh month begins the new year.
While there is no need to connect the new year with the date of creation, the Judeans began to believe that the world or, according to others, humans, was created on the first day of Tishrei. The Bible does not state the date when the world was created. In fact, if the six day events of creation are taken as six periods of time, we can understand the Bible saying that creation was a long process with distinct events happening at different times, so there is no single day of creation. The Talmudic sages knew that we cannot pinpoint a day of creation; they even argued homiletically about whether the world was created in Nisan or Tishrei.
The parent holy day that gave birth to Rosh Hashanah, was Yom Teruah, also called Yom Zichron Teruah, the day of blowing the horn and the day of memorial proclaimed with the blowing of the horn. On the first day of the seventh month Ezra the Scribe gathered the people together and read the Torah, or some of it, to them. Then he said to them: “Go your way, eat rich viands, drink the sweet beverages, and send portions to him who has none prepared: for this day is holy to our Lord; do not be sad; for joy in the Lord is your refuge.” Ezra’s joyous description of how the Judeans should celebrate the first day of Tishrei is in no way similar to the way Rosh Hashanah is celebrated today, nor is it similar to the biblical Yom Teruah.
In Leviticus 23:25, Yom Teruah “shall be a solemn rest to you, a memorial proclaimed with the blowing of horns, a holy convocation. You must do no kind of servile work; and you must bring an offering made by fire to the Lord.” Numbers 29:1–6 supplements this requirement by describing the sacrifices.
Apparently, this day was chosen as a holiday which should be proclaimed to the people by blowing horns because of the number seven. Seven was an important and symbolic number. The ancients saw the number everywhere – such as the body parts, two legs, two arms, two parts of the torso, and the head; and they saw seven heavenly bodies among the stars. The Jews also considered seven important because it reminded them of the existence of God, who created the world in six days, rested on the seventh and gave them laws. Among many other uses of seven, they celebrated the Sabbath on the seventh day and Chag Hamatzot and Sukkot for seven days, marked seven weeks by counting them between Chag Hamatzot and Shavuot and celebrated seven years with a Shemitah Year and seven Shemitahs with the Jubilee year. They celebrated the first day of the seventh month as another reminder of the significance of seven.
Thus we see that the invention of Rosh Hashanah and all of its practices, including the idea that this was a day when Jews should repent was instituted after the period of Ezra the Scribe.
 See Olam Hatanach, Divrei Hayamim, Yechezkeil, page 203.
 Exodus 12:2.
 Babylonian Talmud, Ketubot 57b, yamim (days) can mean years.
 Babylonian Talmud, Chagigah 12a, Rosh Hashanah 8a, 10b-11a, 27a, Avoda Zarah 8a.
 Leviticus 23:23-25; Numbers 29:1-6.
 We do not know the dates of Ezra’s life. He came to Judea some years after some Judeans returned to Judea after the Babylonian exile. He may have come in the fifth century BCE.
 Nehemiah 8:10.