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Day of Atonement
the great annual day of humiliation and expiation for the sins of the nation, “the fast” (Acts 27:9), and the only one commanded in the law of Moses
The way it was observed is described in Leviticus 16:3-10; 23:26-32; and Numbers 29:7-11.
It was kept on the tenth day of the month Tisri, i.e., five days before the feast of Tabernacles, and lasted from sunset to sunset.