In the Written Torah the counting of the months begins from Nisan, making Tishrei the seventh [shevi’i] month. Shevi’i alludes to satiety [sova] and divine abundance [shefa]. This is a month replete with goodness: Rosh HaShana, Yom Kippur, Sukkot, and Shemini Atzeret. We perform many mitzvot in this month, from blowing the shofar to taking the lulav and sitting in the sukka. At the beginning of the month, all human beings stand in judgment before the Creator.

This month is holy, as it is the seventh, and is set aside for many mitzvot. It is what [the Sages] called “mighty in mitzvot” (Rosh HaShana 11a), derived from the verse: “In the month of Etanim [literally, the strong ones]” (I Kings 8:2). Just as the number seven is special compared to the other numbers, so is this month superior to the other months in [the quantity of] its mitzvot, as many mitzvot are performed in it: Rosh HaShana, shofar, Yom Kippur, sukka, lulav, willow branches, and the libation of water.

There is great inspiration [to be found] in this month [as represented by its] astrological sign [Libra]; the scales allude to the function of this day, [Rosh HaShana, on the first day of Tishrei,] when every person is weighed on the scales, so that each individual will be rewarded in accordance with his ways and in accordance with his actions. (Rabbeinu Baĥya ibn Ĥalawa, Kad HaKemaĥ, Rosh HaShana 2)

Further reading: For more on the festivals of Tishrei, see p. 57; A Concise Guide to the Sages, p. 282; A Concise Guide to Halakha, p. 129.