The Day of Atonement, a day when members of God's Church observe a sabbath of rest, fast (no food or water for twenty-four hours), and assemble for services, is rich in meaning. Most of what we know about the meaning of this day comes from Leviticus chapter 16.
In the ceremony God gave to Israel for Atonement, there are two goats. One goat is offered as a sacrifice and the other is sent into the wilderness. God chooses which goat is which. "Then Aaron shall cast lots for the two goats: one lot for the LORD and the other lot for the scapegoat. And Aaron shall bring the goat on which the LORD’s lot fell, and offer it as a sin offering. But the goat on which the lot fell to be the scapegoat shall be presented alive before the LORD, to make atonement upon it, and to let it go as the scapegoat into the wilderness" (Leviticus 16:8-10).
The Church of God understands that the goat that is slain represents Jesus Christ and His sacrifice to pay the penalty for our sins. "Then he shall kill the goat of the sin offering, which is for the people, bring its blood inside the veil, do with that blood as he did with the blood of the bull, and sprinkle it on the mercy seat and before the mercy seat. So he shall make atonement for the Holy Place, because of the uncleanness of the children of Israel, and because of their transgressions, for all their sins; and so he shall do for the tabernacle of meeting which remains among them in the midst of their uncleanness. There shall be no man in the tabernacle of meeting when he goes in to make atonement in the Holy Place, until he comes out, that he may make atonement for himself, for his household, and for all the assembly of Israel" (Leviticus 16:15-17). The goat is slain and its blood sprinkled to make atonement for the sins of the people. This represents Christ. Christ was slain to pay the penalty for our sins in our place (Revelation 13:8, Isaiah 53:1-12). This also connects the symbolism of Atonement with the symbolism of Passover.
But the goat that is turned loose in the wilderness does not represent Christ. That goat is not slain. Yet the sins of the people are placed on the head of that goat also to make atonement for the sins of the people. "But the goat on which the lot fell to be the scapegoat shall be presented alive before the LORD, to make atonement upon it, and to let it go as the scapegoat into the wilderness" (Leviticus 16:10). "Aaron shall lay both his hands on the head of the live goat, confess over it all the iniquities of the children of Israel, and all their transgressions, concerning all their sins, putting them on the head of the goat, and shall send it away into the wilderness by the hand of a suitable man. The goat shall bear on itself all their iniquities to an uninhabited land; and he shall release the goat in the wilderness" (Leviticus 16:21-22). The Day of Atonement falls between Trumpets, representing the return of Christ, and the Feast of Tabernacles, representing the millennial rule of Christ and the saints, and Revelation 20:1-3 helps us understand that the live goat represents Satan: "Then I saw an angel coming down from heaven, having the key to the bottomless pit and a great chain in his hand. He laid hold of the dragon, that serpent of old, who is the Devil and Satan, and bound him for a thousand years; and he cast him into the bottomless pit, and shut him up, and set a seal on him, so that he should deceive the nations no more till the thousand years were finished. But after these things he must be released for a little while." This binding of Satan occurs after the return of Christ (Revelation 11:15-19, 1 Corinthians 15:51-55, Matthew 24:30-31, Revelation 19:11-16) and before the millennium (Revelation 20:4-6), just as the Day of Atonement occurs after the Day of Trumpets and before the Feast of Tabernacles (Leviticus 23:23-36).
Why are two goats necessary to represent atonement for our sins?
Who is responsible for our sins?
There is a shared responsibility. Satan is responsible for our sins because he tempts us into sinning. He deceives us and leads us into sin. Satan is the deceiver of the whole world (Revelation 12:9). He tempts us to sin as he tempted Christ and as he tempted Adam and Eve (Matthew 4:1-3, Mark 1:12-13, Luke 4:1-2, Genesis 3:1-7).
But we also have our share of responsibility for our sins because we choose to sin and to yield to the temptation to sin (Deuteronomy 30:19-20, 1 Corinthians 10:13).
Christ by His sacrifice paid the penalty for our sins, for our share of our guilt, for choosing to yield to temptation and to sin. But Christ did not pay the penalty for Satan's share of the responsibility for our sins. Satan must bear his own guilt for what he has done in leading us to sin. Thus our sins are placed on the head of Satan before he is banished into the bottomless pit as a punishment, represented by the goat being sent into the wilderness (Leviticus 16:21-22, Revelation 20:1-3). Satan's punishment is not death, for angels, including Satan as an angel who sinned, cannot die (Luke 20:36, 2 Peter 2:4). Satan's punishment is the suffering that results from his removal from his position of authority and being cast into the bottomless pit and the Lake of Fire (Revelation 20:1-3, 20:7-10, Matthew 25:41).
Satan is fully responsible for his own sin in a way that mankind is not fully responsible for its sins. Man has sinned partly because Satan has tempted him into sin. But there is no indication that anyone tempted Lucifer into sinning. Every indication from the Bible is that Lucifer committed the first sin. His ways were right until he sinned (Ezekiel 28:14-15). Then, after sinning, his mind became more and more perverted and he acquired a sinful nature (Ezekiel 28:16-17). He became a tempter, and led other angels to sin, and their minds also became evil and twisted, and they became demons (Revelation 12:3-4). Satan has also become the tempter of mankind.
But when Lucifer first sinned, there was no one to tempt him. God did not tempt him, that is, entice him into sin, for God tempts no one (James 1:13). Nor was their any evil demon to tempt Lucifer if Lucifer was the first to sin and then led some of God's angels into sin, who became demons. Nor does it make sense to think that God created an evil nature in Lucifer so he was tempted by his own evil nature to sin. We have human nature with its evil lusts, but that is because Satan puts that nature in us, which is his evil nature, because he sinned first (Revelation 12:9, Ephesians 2:1-3, Jeremiah 17:9).
Every influence upon Lucifer in the beginning must have been a right influence. God must have taught Lucifer and all His angels the right way of life. God would not have created an evil nature in Lucifer, nor was there any other evil being to entice Lucifer into sin if he was the first sinner.
So in the absence of any temptation to do wrong, why would Lucifer sin? Why would he deliberately and coldly, without temptation, choose a way of life that would bring misery upon himself and others? Before he sinned, he had this testimony from God, that he was perfect in his ways (Ezekiel 28:15). He also had wisdom, so he could not have sinned accidentally without knowing what he was doing (Ezekiel 28:12-14). The Bible seems to indicate that violence and vanity were among Lucifer's first sins (Ezekiel 28:16-17). But that still does not indicate WHY Lucifer chose to sin in the first place. God must have taught all the angels the right way of life and must have warned them about the consequences of vanity, teaching them to avoid it. Why would Lucifer, full of wisdom and perfect in his way of life, taught by God, deliberately choose to ignore God's instructions and warnings and choose vanity, to exalt himself?
The Bible does not say specifically, but the only reason I can think of is that Lucifer did not believe God's teachings. He had never known sin, or vanity, or the consequences of sin before he actually sinned, and then it was too late. Part of the penalty of sin is perversion of mind, and once that set in, he could never again think clearly enough to go back. Probably he had never known suffering or unhappiness. Before he sinned, his life must have been joyous. And he must have considered the possibility, despite God's warnings, that if he exalted himself, if he experimented with a little vanity, a little pride, and little self-promotion and getting for the self, it might make him happier. In order to know otherwise, he would have had to have faith and trust in God's word and God's teaching. He did not. He must have doubted God's warnings and teaching. So he tried sin. And once he took that path, there was no turning back. The things God had warned him about took effect. His mind became more and more perverted, twisted, evil, and unhappy.
This may be one reason why God places so much emphasis in the Bible on faith and trust in Him, that we believe what He says. He may have seen how lack of belief destroyed Lucifer. We have to learn to trust and believe God as Lucifer did not.
Lucifer may have been the first one to practice the scientific method of experimentation and observation of results as the ultimate source for truth rather than trusting God and believing what God says. He didn't trust God's revelation. He wanted to experiment with sin to see the results for himself. And it cost him his happiness for all eternity.
Satan has influenced all mankind to practice that same distrust of God and His word, but we, through God's calling, have the opportunity to reject that way of thinking and to learn to have faith in God and what God says. We must have a living faith that inspires us to believe and strive to obey God and all of His instructions and commandments (James 2:17-26).
We must also be careful not to sin willfully after receiving knowledge of the truth, as Satan did. Satan made a decision to disbelieve God and to practice a sinful way of life in rebellion against God. He did not sin accidentally or through personal weakness. We must be careful that we do not sin as he did, deliberately, coldly, with calculated forethought, not through temptation or weakness, choosing once and for all to turn away from God and His way of life after we have received knowledge of God's truth. If we do that, we are in danger of committing the unforgivable sin (Mark 3:28-29, Matthew 12:31-32, Luke 12:10, 1 John 5:16-17, Hebrews 6:4-8, 10:26-31), from which we can never repent.
Some worry that they have committed the unpardonable sin. Mr. Herbert W. Armstrong taught that if we have committed the unpardonable sin, we will not WANT to repent. If we want to repent and turn back to God, we can, because the fact that we want to turn to God and be forgiven and obey Him indicates we have not committed the unpardonable sin, and I tend to agree with that. But nevertheless, we do need to fear committing the unpardonable sin and resolve never to give up on God and turn from Him and His ways permanently, because if we do that, we may never be able to repent from that decision.
Here are links to related sections in Preaching the Gospel:
The Day of Atonement - the Putting Away of Satan, Chapter 2
Passover -- the Sacrifice of Christ, Chapter 2
Faith, Chapter 6
Evolution versus the Creation Account in Genesis, Chapter 1
Our Attitude and Approach Towards God's Word, Chapter 1
How to Understand the Bible, Chapter 1