Yom Kippur, also known as the Day of Atonement, is the most solemn and most Holy holiday on the Jewish calendar.
"Also on the tenth day of this seventh month there shall be a day of atonement: it shall be an holy convocation unto you; and ye shall afflict your souls, and offer an offering made by fire unto the LORD. And ye shall do no work in that same day: for it is a day of atonement, to make an atonement for you before the LORD your God."- Leviticus 23:27-28
Interestingly, It is another Jewish holiday that ends with one long note on the Shofar.
To read an excellent article about the details of this holiday, HERE'S THE LINK
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