Leviticus 23:27 reads, “The tenth day of this seventh month is the Day of Atonement. Hold a sacred assembly and deny yourselves, and present a food offering to the LORD.” So, on Yom Kippur, the nation of Israel were to “deny” themselves as part of the sacred observance.
The Hebrew phrase here can literally be translated “you shall humble your souls.” The same command is found in Leviticus 16:29, and it has traditionally been understood as a reference to fasting or not eating for this day. The “denial” may have involved more than food, however. In the Mishnah, an ancient collection of Jewish traditions, the Day of Atonement forbade food and drink, bathing, using oil to moisten the skin, wearing sandals, and sexual relations.
In modern Judaism, the Day of Atonement takes places on the tenth day of the seventh month on the Jewish calendar and is considered one of two major fasts (the other is Tisha B’Av). There are five minor fast days, as well, for a total of seven fasts in the modern Jewish tradition. However, the Day of Atonement is the only day the Old Testament commanded a fast (or a humbling of the soul).
Leviticus 23:28–32 offers additional insight regarding how the Jews denied themselves on the Day of Atonement: “Do not do any work on that day, because it is the Day of Atonement, when atonement is made for you before the Lord your God. Those who do not deny themselves on that day must be cut off from their people. I will destroy from among their people anyone who does any work on that day. You shall do no work at all. This is to be a lasting ordinance for the generations to come, wherever you live. It is a day of sabbath rest for you, and you must deny yourselves. From the evening of the ninth day of the month until the following evening you are to observe your sabbath.”
Here we find an emphasis on 1) not performing work of any kind, 2) making atonement, and 3) being “cut off” for disobeying this command. This command was an ongoing one; every Day of Atonement was to be a day of fasting and rest. The Day of Atonement was also the one day per year the high priest could enter the Holy of Holies.
Numbers 29:7–11 gives additional instructions for the Day of Atonement: “On the tenth day of this seventh month hold a sacred assembly. You must deny yourselves and do no work. Present as an aroma pleasing to the Lord a burnt offering of one young bull, one ram and seven male lambs a year old, all without defect. With the bull offer a grain offering of three-tenths of an ephah of the finest flour mixed with oil; with the ram, two-tenths; and with each of the seven lambs, one-tenth. Include one male goat as a sin offering, in addition to the sin offering for atonement and the regular burnt offering with its grain offering, and their drink offerings.”
This Day of Atonement was the high holy day of the year, considered the Sabbath of Sabbaths, since no work would take place on that day. To humble one’s soul likely included both fasting from food and from work, allowing God’s people to focus on worship to the Lord through the sacrificial offerings and the atonement of sin.