Though G-d opens the Book of Life on Rosh Hashanah the judgement is not final. The book is 'sealed' on Yom Kippur, ten days later. The time between these two festivals is known as Shabbat Shuva (The Shabbat of Returning). This is a period for self-reflection in which to justify your existence to G-d. Rosh Hashanah is the only Jewish celebration that lasts for two days, signifying the importance of this date in the calendar.