Rosh Hashana
The High Holy Days (the first ten days of the seventh month, also known as Tishre):
The first of these days (also called the Ten Days of Penitence) is the Day of the Blowing of the Ram’s Horn (this is the first day of Tishre, also known as Rosh Hashana, the first of the [New] Year). The day (actually celebrated for two consecutive days) is considered the first of ten Days of Judgment, and is characterized by the blowing of the Ram’s Horn (or shofar) as a means of awakening one’s soul to the need to repent of one’s misdeeds. It is customary to sound a hundred blasts of the horn, of three different styles: one sound, known teqi’a, is a long, more or less unchanging blast; a second sound, known as shevarim, is made up of three considerably shorter blasts; while the third sound, known as teru’a, is actually a long series of short blasts with extremely short pauses between them. It is surmised that the initial use of the ram’s horn blasts was in battle, with the teqi’a used to marshal the forces, shevarim to designate defeat and withdrawal, and tru’a to sound victory.
The hundred blasts sounded in the synagogue on each of the two days of Rosh Hashana are divided up into clusters of blasts, each ethnic Jewish community having its own customs in this regard. The one thing held in common by all is that the initial cluster numbers thirty blasts, which are sounded before the onset of the Additional (Mussaf) Prayer Service.
The third day of Tishre, the day following the two days of Rosh Hashana, is a day of fasting (from early morning to nightfall) in commemoration of the assassination of Gedalya ben Ahiqam, the Babylonian-appointed Jewish governor of Judea after the destruction of the First Temple and of the Davidic monarchy, by the pretender to the Davidic throne. The Babylonian authorities responded by devastating the land of Judea and leading most of its population into exile, thus turning a spiritual calamity into a national one of heroic proportions.
Yom Kippur
The concluding High Holy Day is the Day of Atonement (the tenth day of Tishre, also known as Yom Kippur or Yom Hakippurim), a full 25-hour day of fasting during which time one abstains from food and drink, from wearing leather shoes, as well as from sexual activity, and is the high point of the first ten days of Tishre. This period, from Rosh Hashana to Yom Kippur, which are considered Days of Judgment, is the period during which one's fate for the oncoming twelve months is divinely determined. This period is thus highly recommended for repenting of the sins one has committed against Divine Law, for divine forgiveness, accessible always, is especially available during this period.
Yom Kippur is unique not only in the ways described above; it is the only day of the Jewish year during which one engages in five separate prayer services, which contrast with the three services obligatory on most days of the year and the four services on the other festive days. [It is interesting to note that, much later, Islam adopted the custom of Yom Kippur for everyday implementation, in that Muslims are obliged to pray five times a day, every day of their year.] This fifth prayer service, held in the late afternoon, just before the end of the holy day at nightfall, is known as Ne’ila, or “locking-up”. It is considered to be the very last opportunity to benefit from the divine availability so characteristic of the Ten Days of Penitence, and the synagogues tend to fill to overflowing as Ne’ila begins. It ends with the sounding of the ram’s horn.
The prayers recited on Yom Kippur include Seder Ha’Avoda, a summation of the Temple worship in Jerusalem, culminating in the High Priest chanting the now-forgotten Ineffable Name of the Almighty and with the entire congregation prostrating itself on the ground upon hearing this Name.