And the Lord spoke to Moses, saying, “Now on the tenth day of this seventh month is the Day of Atonement. It shall be for you a time of holy convocation, and you shall afflict yourselves and present a food offering to the Lord. And you shall not do any work on that very day, for it is a Day of Atonement, to make atonement for you before the Lord your God. For whoever is not afflicted on that very day shall be cut off from his people. And whoever does any work on that very day, that person I will destroy from among his people. You shall not do any work. It is a statute forever throughout your generations in all your dwelling places. It shall be to you a Sabbath of solemn rest, and you shall afflict yourselves. On the ninth day of the month beginning at evening, from evening to evening shall you keep your Sabbath. Leviticus 23:26–32, ESV
Yom Kippur, also known as Day of Atonement, is the holiest day of the year for the Jewish people. It takes place on the 10th day of the seventh month (Tishri) on the Jewish calendar. Please carefully read the passage I placed at the top of this post. Do you see the serious emphasis God places on the need for His people’s atonement? What is this atonement? Biblical atonement is the act of God canceling the debt of His people’s sin. Without it God’s wrath against their sin could not be appeased.