Why is the Jewish New Year celebrated in modern times in Tishri, the seventh month, not in Nisan, which is specified as the first month in Exodus?
There is no mention of a New-Year Day in the Jewish Tanakh (Old Testament). However, in Exodus 12:2, God commanded the Children of Israel to observe the month of Nisan—the month in which the annual Passover occurs—as the first month. It can be inferred from that commandment that the Jewish New-Year Day was to be the first day of Nisan, which in modern times has 30 days that span our Gregorian months of March and April.
In other words, the Jewish festival calendar began in Spring for the ancient Hebrews. If you have Jewish friends, however, you will have noticed that they celebrate the modern Jewish New-Year Day in the Fall. To be exact, it is observed on the first day of the Jewish month of Tishri, which is the seventh month on the Jewish festival calendar.
Why the change from first day of Nisan to first day of Tishri?
I can only speculate, but once again having a correct chronology for the Hebrew kings seems to provide a logical explanation for the change in the observance of the Jewish New-Year Day from Spring to Fall. As my harmonization of the reigns of the Hebrew kings demonstrates, the change can be explained by the way the ancient kingdoms of Israel and Judah accounted the years in the reigns of their kings.
After the united Kingdom of Israel divided into the northern kingdom of Israel and the southern kingdom of Judah in the fifth year of Rehoboam, the two kingdoms observed different ways of recording the reigns of their kings. Israel counted the years of its kings starting from the first day of Nisan, the biblically specified first month that featured the Passover. Judah counted the years of its kings starting from the first day of Tishri, the seventh month that featured the Day of Atonement.
The northern kingdom of Israel and its observance of the New-Year Day on the first day of Nisan came to an end in 721 BCE at the hand of the Assyrians. On the other hand, the southern kingdom of Judah, with the observance of its New-Year Day on the first day of Tishri, continued to function as a Jewish state for another 136 years.
When Nebuchadnezzar II of Babylon carried the people of Judah into Exile after the destruction of Judea, Jerusalem, and the Temple of Solomon in 586 BCE, the New-Year Day celebrated on the first day of Tishri is the observance that went into Exile with the Jews of Judah, and was no doubt the custom observed during the years of Exile in Babylon.
When the Jewish remnant was allowed to return to Jerusalem and Judea from Babylon circa 536 BCE, they brought their customs—including their New-Year Day celebration on the first day of the seventh month Tishri—with them, and the Jewish New Year has apparently been observed by Jews on the first day of Tishri down through the centuries to the present day.
The modern Jewish New Year is called Rosh Hashanah, which means literally “Head of the Year,” and is celebrated in the Fall on the first day of Tishri, always on a date in late September or early October on the Gregorian calendar we use today.
