Today is the Day of Atonement, which concludes the High Holy Days. The 1901-06 Jewish Encyclopedia (which might be comparable in tone and content to the 1914 Catholic Encyclopedia, but still fascinating if outdated in some respects) is online. Here is part of the entry on Yom Kippur:
In rabbinic Judaism the Day of Atonement completes the penitential period of ten days ( ) that begins with New-Year’s Day, the season of repentance and prayer; for though prayerful humiliation be acceptable at all times, it is peculiarly potent at that time (R. H. 18a; Maimonides, “Yad,” Teshubah, ii. 6). It is customary to rise early (commencing a few days before New-Year); the morning service is preceded by litanies and petitions of forgiveness (, “seliḥot”) which, on the Day of Atonement, are woven into the liturgy (Shulḥan ‘Aruk, Oraḥ Ḥayyim, 581; Zunz, “S. P.” 76 et seq.). New-Year’s and Atonement days are days of serious meditation (, “awful days,” Zunz, “S. P.” 82, note). The former is the annual day of judgment (), when all creatures pass in review before the searching eye of Omniscience (R. H. i. 2). According to the Targum, the day of the heavenly session in Job i. 6 et seq. was no other than the first of the year (, resh shatta; see also Zohar Ex. 32b, ed. Wilna, 1882). Accordingly, the Divine Judge receives on that day the report of Satan, arch-fiend and accuser in heaven; the other angels, it is presumed, are friendly to the accused, and plead their cause before the august tribunal. The sounds of the “shofar” are intended to confuse Satan (R. H. 16b). There is, indeed, in heaven a book wherein the deeds of every human being are minutely entered (Abot ii. 1, iii. 16; a book of record, “book of remembrance,” is alluded to, Mal. iii. 16). Three books are opened on the first day of the year, says the Talmud (R. H. 16b); one for the thoroughly wicked, another for the thoroughly pious, and the third for the large intermediate class. The fate of the thoroughly wicked and the thoroughly pious is determined on the spot; the destiny of the intermediate class is suspended until the Day of Atonement, when the fate of every man is sealed (R. H. 16a).
Here is the Wikipedia entry.