The [post-biblical] development of the High Holy Days may be traced through sources compiled in the period following the destruction of the Second Temple (in the year 70 CE)and later recorded in the Mishnah (edited in 200 CE by Rabbi Judah the Prince). How much of the material was created only after the destruction and how much may have been produced earlier is a matter for conjecture. One should note, however, that discussions about the prayers of Rosh Hashanah are already recorded in the teachings of the schools of Hillel and Shammai, which would date these materials to the first century CE.
More significant is the specific designation in these sources of the first day of the seventh month, Tishrei, as Rosh Hashanah, the beginning of the year, and a definition of what this title means: “The first of Tishrei is the beginning of the year [Rosh Hashanah] for years, sabbatical cycles, and the jubilee?” (Mishnah, Rosh Hashanah 1.1). That is, the first of the seventh month was the time to begin the numbering of the year and the counting of the years for the seven‑year cycle (the sabbatical) and the 50‑year cycle (the jubilee).
Of greatest import, however, is the information given in the Mishnah about the role of judgment on the first of Tishrei, now designated simply “Rosh Hashanah”:
“On Rosh Hashanah all human beings pass before Him as troops, as it is said, “the Lord looks down from heaven, He sees all mankind. From His dwelling place He gazes on all the inhabitants of the earth, He who fashions the hearts of them all, who discerns all their doings” (Ps. 33:13‑15) (Mishnah, Rosh Hashanah 1.2).
The Mishnah also describes the basic prayers and shofar‑blowing practices for Rosh Hashanah, which form the heart of the synagogue service today (Mishnah, Rosh Hashanah 4.5‑6; 4.9). The three major themes of the day‑-kingship, remembrance, and shofarot–are also established in the Mishnah, as are specific regulations concerning the sounding of the shofar during the prayers (Mishnah, Rosh Hashanah 4.5).
Pronounced: MISH-nuh, Origin: Hebrew, code of Jewish law compiled in the first centuries of the Common Era. Together with the Gemara, it makes up the Talmud.
Pronounced: roshe hah-SHAH-nah, also roshe ha-shah-NAH, Origin: Hebrew, the Jewish new year.
Pronounced: sho-FAR or SHO-far, Origin: Hebrew, a ram’s horn that is sounded during the month of Elul, on Rosh Hashanah, and on Yom Kippur. It is mentioned numerous times in the Bible, in reference to its ceremonial use in the Temple and to its function as a signal-horn of war.
Pronounced: TISH-ray, Origin: Hebrew, Jewish month, usually coinciding with September-October.