Leviticus 16 regulates the most important day of the year for the nation of Israel, the Day of Atonement. Modern Jews still celebrate this day and call it Yom Kippur. After the initial anointing ceremony of the tabernacle (Lev 8-10), this would be the only day each year that anyone could enter the inner room of the tabernacle, the Holy of Holies. Take a look at the illustration of the tabernacle and its surroundings again to see where the Holy of Holies is located with respect to everything else: http://www.karbelmultimedia.com/portfolio/the-tabernacle/
In verses 1-2, God explains to Moses and Aaron that the high priest cannot enter the Holy of Holies whenever he wants. Just as Nadab and Abihu died, so shall the high priest die if he enters the Holy of Holies on any other day of the year, other than the Day of Atonement.
God instructs Aaron how to prepare himself for the sacrifices he will make on this day in verses 3-6. Aaron will need a bull for a sin offering (to atone for the sins of Aaron and his household) and a ram for a burnt offering. He was not to wear the normal high priestly garments, but a simpler wardrobe that would symbolize the humility of the nation who was coming before God to ask forgiveness. Aaron would also need two goats and a ram as offerings from the people of Israel.
In verses 7-10, we learn that one goat would be chosen to be sacrificed as a sin offering, but the other, the scapegoat, would be sent into the desert to atone for the sins of the nation. The scapegoat would leave the camp of Israel, and never return, symbolizing how the sins of Israel from the previous year had been removed and would never return again.
Verses 11-14 describe the ceremony in detail. First, Aaron must present the bull as a sin offering for himself and his household. The high priest cannot present an offering for the sins of the people until he has first atoned for his own sins. The blood of the bull had to be taken into the Holy of Holies and sprinkled on the cover of the Ark of the Covenant, also called the “mercy seat.”
Before Aaron enters, he must burn incense and allow the incense to fill the Holy of Holies so that Aaron will be protected from the direct presence of God, who is “located” above the Ark.
In verse 14, Aaron is instructed how to sprinkle the blood of the bull on the Ark. Commentator Mark Rooker, in Leviticus: An Exegetical and Theological Exposition of Holy Scripture (The New American Commentary)
Aaron was to sprinkle the blood of the bull with his finger on the front of the mercy seat seven times. This transporting and sprinkling of blood in the Most Holy Place [Holy of Holies] is the most unique feature of the Day of Atonement. This was the only occasion in which blood was brought into the Most Holy Place, which underscores the singular solemnity of this preeminent day. The mercy seat covered the ark, which contained the Ten Commandments, manna, and Aaron’s rod (Heb 9:4–5). The narrative accounts surrounding these items stress the rebellion of the Israelites. Thus the cherubim looking down upon the mercy seat saw only the evidence of Israel’s unfaithfulness. The blood on the mercy seat indicated that Israel’s sin was atoned for by a substitutionary death.
Next, in verses 15-19, the blood from the goat offered for the people of Israel is also sprinkled on the Ark. Because the sins of the people are so pervasive, the goat blood is then sprinkled on every object within the tabernacle, inner room and outer room. In addition, the altar for burnt offerings in the tabernacle court must also be purified with the blood of the bull and goat. In this way, the tabernacle and its courtyard is cleansed of all impurity brought by the people of Israel into God’s earthly home.
Once the blood atonement has been performed, Aaron is to move on to the scapegoat. Verse 21 states clearly the procedure: “He is to lay both hands on the head of the live goat and confess over it all the wickedness and rebellion of the Israelites—all their sins—and put them on the goat’s head. He shall send the goat away into the desert in the care of a man appointed for the task.”
Notice that the scapegoat is to remove all the sins of Israel from the preceding year. The Day of Atonement is comprehensive, and thus significant for the people of Israel. Even though sacrifices and offerings have been happening every day in the tabernacle courtyard, they are not sufficient to remove all the sins of Israel. One day a year is set aside to wipe the slate clean.
Why are two goats required for the Day of Atonement? Mark Rooker remarks,
In the Day of Atonement ceremony the first [goat] pictures the means for atonement, the shedding of blood in the sacrificial death. The scapegoat pictures the effect of atonement, the removal of guilt. What is accomplished in the scapegoat ritual is expressed by David in the Psalms: ‘As far as east is from west, so far has he removed our transgressions from us’ (Ps 103:12).
After the scapegoat is sent away, Aaron has a couple more things to do. He must remove his garments and bathe. Once he has bathed, he is to put back on his normal high priestly garments. He must then sacrifice the burnt offering for himself and the people of Israel. The man who escorts the scapegoat must also bathe himself before re-entering the camp.
Verses 29-34 also instruct the people of Israel that on the Day of Atonement, they are to deny themselves. Jewish tradition holds that they were not to work, eat, bathe, use body oil, have sex, or wear shoes. All of these were hardships to remind them of their humility before God. God mandates that the Day of Atonement is a lasting ordinance to be performed on the same day every year.