Albert Barnes Commentary Leviticus 16:29

"And it shall be a statute for ever unto you: in the seventh month, on the tenth day of the month, ye shall afflict your souls, and shall do no manner of work, the home-born, or the stranger that sojourneth among you:" — Leviticus 16:29 (ASV)

Seventh month, on the tenth day - The month Ethanim or Tisri, being the seventh in the Sacred year, has been called the sabbatical month. On the first day, the Feast of Trumpets was celebrated (Leviticus 23:24); the tenth day was the Day of Atonement, and on the fourteenth day, the Feast of Tabernacles commenced (see note on Leviticus 23:24; Exodus 23:16).

Afflict your souls - This is the old term for fasting, but its meaning evidently embraces not only abstinence from food but also the penitence and humiliation that give scope and purpose to the outward act of fasting. The Day of Atonement was the only public fast commanded by the Law of Moses. See further directions in Leviticus 23:27-32. Regarding fasts observed in later times, see Zechariah 8:19 and the margin reference.

A stranger that sojourneth among you - This means, rather, the foreigner who dwells among you (see note on Exodus 20:10). The meaning is one of foreign blood, who dwelt with the Israelites, had renounced false gods, and had become familiarly known to his neighbors—for example, the Kenites (Judges 4:11, etc.), the Gibeonites (Joshua 9:0), and a considerable portion of the “mixed multitude” (compare Exodus 12:38 and Exodus 12:48). Since the foreigner had the blessing and protection of the Law, he was bound to obey its statutes.