From the Resurgence blog, a good summation of very important day:
Yom Kippur is also known as the Day of Atonement, which is the climax of the Old Testament sacrificial system and is the most solemn day on the Jewish calendar. It was a day of great bloodshed and a day on which the gravity of humanity’s sin could be seen visibly. Because of its importance, it eventually became referred to simply as “the Day.”
The Center of the Pentateuch
The primary section in Scripture concerning the Day of Atonement appears in Leviticus 16-17. This passage functions as the center of the book of Leviticus, which is itself the center of the Pentateuch. This day speaks of the Lord’s gracious concern both to deal fully with his people’s sin and to make them fully aware that they stand before him, accepted and covered in respect of all iniquity, transgression, and sin (Lev 16:21).
On this day, the high priest would enter the Holy of Holies to atone for the sins of Israel in order to avert the holy wrath of God for the sins of the past year and to remove their sin and its stain from them. Two healthy goats without defect were chosen. They were therefore fit to represent sinless perfection.
Two Images of the Atonement
The first goat was a propitiating sin offering. The high priest slaughtered this goat, which acted as a substitute for the sinners who deserved a violently bloody death for their many sins.
Then the high priest, acting as the representative and mediator between the sinful people and their holy God, would take the second goat and lay his hands on the animal while confessing the sins of the people. This goat, called the scapegoat, would then be sent away to die in the wilderness away from the sinners, symbolically expiating or removing the sins of the people by taking them away.
The sacrifices of the Day were designed to pay for both sin’s penalty and sin’s presence in Israel. The shedding of blood and the sending off of the scapegoat were meant to appease God’s wrath against sin and to cleanse the nation, the priesthood, and even the sanctuary itself from the taint of sin (Lev 16:30).
The Lamb of God
The Day of Atonement was a foreshadowing of Jesus, the Lamb of God who takes away the sins of the world, and our great High Priest who is able to sympathize with us in our weakness. These great images of the priest, slaughter, and scapegoat are all given by God to help us more fully comprehend Jesus’ bloody sacrifice for us on the cross.
Jesus’ fulfillment of the Day of Atonement is why we are forgiven for and cleansed from our sins. To preach anything else is to proclaim a “different gospel,” which is no gospel at all (Gal 1:6-7). Spurgeon drives this point home: “Many pretend to keep the atonement, and yet they tear the bowels out of it. They profess to believe in the gospel, but it is a gospel without the blood of the atonement; and a bloodless gospel is a lifeless gospel, a dead gospel, and a damning gospel” (Sermon 1667).
Jesus Christ fulfills and accomplishes forever what the two goats symbolized. The Old Testament sacrifice of animals has been replaced by the perfect sacrifice of Christ (Heb 9:26, 10:5:10; 1 John 2:1-2 and4:9-10). Christ paid sin’s penalty (Rom 3:25-26 and 6:23; Gal 3:13). He redeemed us (Eph 1:7), paying the price that sets us free (1 Cor 6:20;Gal 5:1). He turned away God’s wrath (Rom 3:25) and reconciled believers to God (Eph 2:16) so we can be forgiven for our sins and cleansed from all unrighteousness (1 John 1:9).