The Day of Atonement was instituted after Aaron’s sons, Nadab and Abihu, were killed in the sanctuary of God. The Day of Atonement occurred once a year. On this day—and only on this day—the high priest entered the inner part of the Tabernacle where the Ark of the Covenant sat to make atoning sacrifices for the sins of all the Israelites. It was a solemn occasion for all Israelites, marked by rest and fasting. Today, this commemoration is known as Yom Kippur.