Charles Ellicott Commentary Leviticus 23:27

"Howbeit on the tenth day of this seventh month is the day of atonement: it shall be a holy convocation unto you, and ye shall afflict your souls; and ye shall offer an offering made by fire unto Jehovah." — Leviticus 23:27 (ASV)

Also on the tenth. — See Leviticus 16:29.

And ye shall afflict your souls. — That is, fast. (See Leviticus 16:29.)

And offer an offering. — See Numbers 29:8-11.