Fasting, a voluntary abstinence from food, is a principle of the gospel of Jesus Christ for developing spiritual strength; it has always existed among true believers. Without doubt it was practiced by Adam and his posterity from the beginning whenever they had the gospel among them. The early portion of the Old Testament does not mention fasting, but this is due to the scarcity of the record rather than the absence of the practice. There are frequent references to fasting in the later portions of the Old Testament and in the New Testament.
The Day of Atonement appears to be the only fast ordered by the law. Other fasts were instituted during the exile (Zech. 7:3–5; 8:19); and after the return, fasting is shown to be a regular custom (Luke 5:33; 18:12). It was regarded as a natural way of showing sorrow. Along with the fasting were often combined other ceremonies, such as rending of the garments, putting on sackcloth, refraining from washing the face or anointing with oil (2 Sam. 12:20; 1 Kgs. 21:27; Isa. 58:5). All such observances were, of course, liable to become mere formalities, and the danger of this was recognized by the prophets (Isa. 58:3–7; Joel 2:12–13; Zech. 7:5–6; see also Matt. 6:16–18).
The Day of Atonement was the 10th day of the seventh month. The directions for its observance are given in Ex. 30:10; Lev. 16; 23:26–32; Num. 29:7–11. The day was kept as a national fast. The high priest, clothed in white linen, took a bullock as a sin offering and a ram as a burnt offering for himself and his house; and two he-goats as a sin offering and a ram as a burnt offering for the congregation of Israel. He presented the bullock and the two goats before the door of the tabernacle. He then cast lots upon the two goats. One was to be for the Lord for a sin offering. The other was for Azazel (the completely separate one, the evil spirit regarded as dwelling in the desert), to be sent away alive into the wilderness. He then killed the bullock, his own sin offering, and, taking a censer full of live coals from off the brazen altar with two handfuls of incense into the Holy of Holies, cast the incense on the coals there so that the cloud of smoke might cover the mercy seat and, as it were, hide him from God. He then took of the blood of the bullock and sprinkled it once on the east part of the mercy seat (as an atonement for the priesthood) and seven times before the mercy seat (as an atonement for the Holy of Holies itself). Then he killed the goat, the congregation’s sin offering, and sprinkled its blood in the same manner, with corresponding objects. Similar sprinklings were made with the blood of both animals (bullock and goat) on the altar of incense (Ex. 30:10; Lev. 16:15) to make an atonement for the Holy Place. No one besides the high priest was allowed to be present in the tabernacle while these acts of atonement were going on. Lastly, an atonement was made for the altar of burnt offering in a similar manner. The goat for Azazel was then brought before the altar of burnt offering. Over it the high priest confessed all the sins of the people of Israel, after which it was sent by the hand of a man into the wilderness to bear away their iniquities into a solitary land. This ceremony signified the sending away of the sins of the people now expiated to the Evil One to convince him that they could no more be brought up in judgment against the people before God. Then the high priest took off his linen garments, bathed, put on his official garments, and offered the burnt offerings of two rams for himself and his people.
In Heb. 9:6–28 a contrast is drawn between the work of the high priest on the Day of Atonement and the work of Christ, the great High Priest, who offered once for all the perfect sacrifice of Himself. The sacrifices provided an annual “remembrance” of sin (Heb. 10:3–4), while the sacrifice of Christ removes the sin and leads to the complete sanctification of the believer (9:12, 14, 26; 10:10–18).
Fasting is confirmed in latter-day revelation as an ancient practice, but more significantly, the spiritual benefits are described more fully than in the Bible. The Book of Mormon, especially, is a fruitful source of information. See Alma 5:46; 6:6; 10:7; 17:3, 9; 28:6; 30:2; 45:1; Hel. 3:35; 9:10; 3 Ne. 27:1; 4 Ne. 1:12; Moro. 6:5; also D&C 59:14; 88:76.