Or HaChaim on Leviticus 23:28/אור החיים על ויקרא כ״ג:כ״ח

1 וכל מלאכה לא תעשו, "and you must not perform any work." The unusual way the Torah explains the reason for the work prohibition may be understood in light of something we have been taught in Sotah 40. The Talmud there states that the congregation is not to recite verses from scripture while the priests are pronouncing the blessing, as it would be equivalent to a slave receiving a blessing from his master while not even bothering to listen. We may understand the legislation here in a similar manner. Seeing that the Day of Atonement itself confers a blessing, i.e. forgiveness, it would be most inappropriate to observe "business as usual" on such a day. It is more appropriate to spend one's time contemplating the grandeur of the Lord of the universe who has set aside a day on which His creatures are rehabilitated.