The focus in these verses is on the spirit or attitude in which we keep Atonement. Considering verse 29, doing things right on this day is a serious responsibility. For religious Jews, this is the most solemn day of the year.
Three times in this short span of verses God commands us to afflict our souls or be afflicted. Many think that "fast" is derived from the same word as "afflict," but such is not the case. They are not cognate; in the Hebrew they have no etymological connection. They are two different words with distinctly different roots. God probably uses these different words to emphasize the attitude one should have during a fast, rather than the act itself, because it is entirely possible for a person to fast for a day and not be in the right attitude. However, when done properly, fasting can very greatly enhance the lesson of this holy day.
"Fast" is derived from a word meaning "to cover the mouth," implying that no nourishment gets past it into the body.
"Afflict," anah, is an intriguing word, giving us great insight into how God intends us to use this day. According to The Theological Wordbook of the Old Testament, its primary meaning is "to force or try to force into submission," "to punish or inflict pain upon." When used in contexts involving attitude, it means "to find oneself in a stunted, humble, lowly position; cowed." It is used to describe what one does to an enemy (Numbers 24:24), what Sarah inflicted on Hagar (Genesis 16:6), and what the lawless do to the weak (Exodus 22:22). It is used of the pain inflicted on Joseph's ankles by his chains (Psalm 105:18). Moses describes Egypt's treatment of Israel with this word (Exodus 1:11-12), and in this case, it implies more than the emotional pain of slavery but something that hurt physically. Thus, in Strong's Concordance, the author uses such forceful and painful words as "browbeat," "deal hardly with," "defile," "force," "hurt," and "ravish" to describe it. Anah is a strong, forceful word.
John W. Ritenbaugh
Pride, Humility, and the Day of Atonement