Answer:
For many secular Jews, the period is an opportunity to reconnect with family members or get in touch with cultural traditions — they’re by far the best-attended holidays at most synagogues. But the theological import of the holiday and the different ways it has changed or solidified over time can tell us a lot about the development of Jewish culture and values: the story of a group of people for whom the tension between assimilation and preserving tradition has long been a major part of their culture.
The period between Rosh Hashanah and Yom Kippur is known as the “Ten Days of Repentance” (“Aseret Yemei Teshuvah”). According to traditional Jewish teaching, God opens the Book of Life each year on Rosh Hashanah to inscribe a person’s fate for the coming year, but does not seal that fate until Yom Kippur, the “Day of Atonement.” The Days of Repentance thus offer an observant Jew the opportunity to atone for past misdeeds, seek forgiveness, and mend his or her behavior through the practice of teshuvah, or “return.”
Thus, a popular form of well-wishing throughout the holiday period is to wish that somebody be “written in the Book of Life.”
Prayers on Rosh Hashanah and Yom Kippur, as well as the intervening period, often take the form of recognizing and confessing past deeds. For example, the shorter Vidui Ashamnu (“we are guilty”) prayer is recited or sung repeatedly throughout the period, while the longer Al-Cheyt is sung only on Yom Kippur itself.