Yom Kippur, also known as the Day of Atonement, is the only one of God's commanded holy days where a fast is required. No work whatsoever may be done on the day.
The tenth day of the seventh month is the day when the annual ritual is to be performed to take away the sins of the people. On that day do not eat anything at all; come together for worship, and present a food offering to the Lord.
28 Do no work on that day, because it is the day for performing the ritual to take away sin. 29 Any who eat anything on that day will no longer be considered God’s people. 30 And if any do any work on that day, the Lord himself will put them to death. 31 This regulation applies to all your descendants, no matter where they live. (Leviticus 23)
Is atonement important?
22. Now almost all things are purified with blood according to the law, and without the shedding of blood there is no remission of sins. (Hebrews 9:22, HBFV)
What does it mean?
Before Aaron goes into the Most Holy Place, he must take a bath and put on the priestly garments . . . 5 The community of Israel shall give Aaron two male goats for a sin offering and a ram for a burnt offering. 6 He shall offer a bull as a sacrifice to take away his own sins and those of his family. (Leviticus 16:4-6, TEV)
In the symbolism of this day Aaron, the brother of Moses, represents Christ. The Most Holy Place, also known as the 'Holy of Holies," represents God's throne in heaven. Since Aaron, as a human being, is of himself unqualified to stand before God he must be ceremonially cleansed and have his sins forgiven.
8 There he shall draw lots, using two stones, one marked 'for the Lord' and the other 'for Azazel.' 9 Aaron shall sacrifice the goat chosen by lot for the Lord and offer it as a sin offering. 10 The goat chosen for Azazel shall be presented alive to the Lord and sent off into the desert to Azazel, in order to take away the sins of the people. 26 The man who drove the goat into the desert to Azazel must wash his clothes and take a bath before he comes back into camp. (Leviticus 16:8, 10, 26, TEV)
The priest, in this case Aaron, must cast lots to determine which of two goats will symbolize the Lord and which will symbolize the devil. Casting lots is an ancient way of allowing God to decide something rather than imperfect man. The goat for the Lord represents Christ taking away our sins.When the high priest enters the veil of the holy of holies the goat's blood sprinkled on the mercy seat of the ark of the covenant represents Christ, on the Sunday after his resurrection, presenting himself to God in heaven.
25. Therefore, He has the power throughout all time to save those who come to God through Him because He is ever living to intercede for them. 26. For it is fitting that we should have such a High Priest Who is holy, blameless, undefiled, set apart from sinners and made higher than the heavens; (Hebrews 7, HBFV)
After the ceremonies on Atonement are completed, the person who released the Azazel goat must wash their clothes. After symbolically coming in contact with Satan he must cleanse himself.
13. Now go and learn what this means: 'I desire mercy and not sacrifice.' For I did not come to call the righteous, but sinners to repentance." (Matthew 9:13)
6 'The kind of fasting I want is this: Remove the chains of oppression and the yoke of injustice, and let the oppressed go free. 7 Share your food with the hungry and open your homes to the homeless poor. Give clothes to those who have nothing to wear, and do not refuse to help your own relatives.' (Isaiah 58:6-7)
Fasting means going without food or water for a period of time. On the day of Atonement believers fast for a full 24 hour period. The primary reasons Christians fast on Atonement:
Fasting on the day is commanded by God
Fasting focuses our mind on what GOD is doing
Fasting helps awaken in us mercy and compassion