Jesus' existence both as a man and as God, uniquely allowed Him to reconcile mankind with God. Being a man allowed Him to die as an appropriate substitute for humankind (because He was a human), and as God allowed Him to live the perfect life beforehand, and to bear the punishment He incurred as our substitute. As a result of Jesus' death, where all the punishment that sinful humankind deserves was placed on Him, by faith we can take His righteousness upon ourselves. And if, through faith, we take Christ's righteousness upon ourselves, God then sees us as righteous - He sees us as perfect, because (metaphorically) we have been washed clean by Jesus' blood.
There is no clear and concise teaching on the nature of the atonement in any one place within the Bible. It is interesting that, central though the atonement is to the Christian faith, the Church never established a set statement of the way in which Christ saved believers.
In the early Church, much discussion centered on other issues such as the Trinity; consequently, the atoning work of Christ was merely accepted and somewhat ignored. However, this situation did not last long and throughout the history of the Church, several soteriological theories (theories of the atonement) received prominence - some of these quite embarrassing.
I believe, after studying the teaching of the atonement within the Bible and major theories, that God's word is clear that Jesus' death was one of a vicarious sacrifice; that is, on the cross, He was a substitute for mankind, taking the punishment for man's sin, diverting God's wrath and allowing the forgiveness of the repentant through faith in Him. This is the view I will support with Biblical evidence below.
I have also written a study on the Atonement (that includes what I believe to be erroneous theories), found here (pdf, 100k, 5,300 words).
Due to the many references to sacrifices and atonement with respect to Christ and predating Christ in the Old Testament, we'll begin with a look at the teaching of these in the Old Testament.
(This section studied in more detail here.)
It is a common misconception that the means of salvation is different in each of the Testaments: New Testament religion is grace, while Old Testament religion is law. This is simply not the case. Salvation in the Old Testament is by grace as it is in the New Testament.
From a study of the Old Testament view of atonement (found here) we find several points:
It appears that this truth was only partially grasped within the Israelite community before and during Jesus' time, as the existence and extent of legalism recorded in the Bible and other sources indicates that a common belief was that observance of the law earned a right standing with God, whereas we have seen that it is by grace that they were saved, but by observing the law that they remained within God's covenant.
There were several classes of sacrifices within the Old Testament: gift offerings (to express homage and thanksgiving), burnt offerings (usually on behalf of the community as a whole), and sin and guilt offerings (to deal with unintentional offences against God for which the worshipper sought pardon). Central to the whole sacrificial system was the shedding of blood of a ritually clean substitute, which through trusting in God's grace, and through God's grace only, brought appropriation of the covenant blessings to the offerer. The need for the shedding of blood also ingrained an understanding of the holiness of God, and the consequences of sin.
For believers in the Old Testament period as for believers in the New Testament period, salvation is by the blood of Christ: "Day after day every priest stands and performs his religious duties; again and again he offers the same sacrifices, which can never take away sins. But when this priest [Jesus] had offered for all time one sacrifice for sins, he sat down at the right hand of God." (Hebrews 10:11-12)
The study of the Old Testament has led us to the conclusion that salvation for the Israelites was achieved through:
And so it is at this point that we meet one of the offices of Christ - these are the roles that He performed. We'll see that Christ fulfills the needs spoken of in the Old Testament once and for all: He is a priest that makes a sacrifice that lasts for all time and removes the need to offer any sacrifices again. He also comes as a prophet to tell the people God's word, and as a King to rule over the church and indeed the universe.
In the Old Testament, priests were appointed by God to offer sacrifices for the people. They also offered prayers and praise to God on behalf of the people. In so doing, they made the people acceptable to come before God (although only in a limited way in the Old Testament). In the New Testament, Jesus is represented as our Great High Priest, for several reasons:
There were many prophets throughout the OT (such as Moses, Isaiah etc.), and their main role was to deliverer God's word and will to His people, and to be His representative on earth. In this respect, Jesus is seen as a prophet, as He indeed brought revelation of God's word and represented Him on the earth.
There were some who referred to Him as a prophet (Matt. 16:14; Luke 7:16 etc.), but it must also be seen that He is more than a prophet. The author of the letter to the Hebrews had clear opportunity to claim Jesus as a prophet above other prophets, but instead chose to exclaim: "In the past God spoke to our forefathers through the prophets at many times and in various ways, but in these last days he has spoken to us by his Son, whom he appointed heir of all things, and through whom he made the universe" (Hebrews 1:1-2). Similarly, after concluding the section on the superiority of the son, the author could have said, "therefore consider Jesus the greatest prophet of all", but instead concluded "Therefore...fix your thoughts on Jesus, the apostle and high priest whom we confess." (Heb. 3:1).
Although Christ was a prophet, fulfilling all prophetic duties, such a distinction is drawn as Christ as Son of God is far greater than any of the OT prophets: He is the one about which they prophecied; and Jesus was not merely the source of revelation from God, but was the revelation from God. So, rather than saying, as did all the OT prophets, "Thus saith the Lord", Jesus said, "I say unto you..." (e.g., Matt. 5:22).
Though Jesus was born to be the King of the Jews, He refused any attempt by people to establish an earthly kingdom with Him as its king. He told Pilate, "My kingdom is not of this world. If it were, my servants would fight to prevent my arrest by the Jews. But now my kingdom is from another place." (John 18:36).
The Kingdom to which Jesus referred is the Kingdom of God, and is spiritual in nature. When Jesus rose from the dead, God gave Jesus greater authority over the church and over the universe, He sits at God's right hand, and will come again in glory to judge the living and the dead. At that time His authority will be more fully recognised: He will be acknowledged as King of kings and Lord of lords (Rev. 19:16), and every knee will bow to Him (Phil. 2:10).
As sinners, all people had four needs that were met in Christ:
These four needs are met by Christ in the following ways:
Therefore Christ, as fully man was the substitute for mankind in taking the penalty and God's wrath for our sin. As fully God and fully man His death reconciled those who have faith in Him to God.