It has been said that the theme of Redemption runs as a scarlet thread throughout the Bible. The red color of the thread is, of course, indicative of the consummation of that redemption for man, as Christ shed his crimson blood upon the cross for our sins.
The purpose of scripture is to reveal that redemptive scheme, that man may know what God has done, and what he must do to obtain salvation. Various theories have conspired to cloud the clear teaching of scripture. However, with care we can study the Bible, and as Paul wrote, ...by which, when you read, you may understand my knowledge in the mystery of Christ. (cf. Ephesians 3:4).
The term Redemption comes from a Greek word which literally means a loosing, particularly by paying a price. As Unger explains, it is:
One of the other conceptions relating to the necessity for redemption is the implication that if redemption is necessary, there must first be a bondage, which is described in scripture clearly as the consequence of sin against God. God promised Adam and Eve in the beginning that if they disobeyed His command to refrain from eating the fruit of the tree of knowledge, they would surely die (cf. Genesis 2:17).
Paul, thousands of years later commented on their disobedience, by writing, For since by man came death, by Man also came the resurrection of the dead. For as in Adam all die, even so in Christ all shall be made alive (1 Corinthians 15:21-22). In this, both the bondage is made clear (death through sin), as is the redemption (life in Christ).
It is important to understand the reality of this great penalty for sin. Paul wrote first, for all have sinned and fall short of the glory of God (Romans 3:23), and later, For the wages of sin is death... (Romans 6:23). It is because of our sin that Christ had to die. The penalty of sin is death, and our death could be avoided only if the penalty was paid by another.
The death of animals by sacrifice, a staple of Old Testament worship, was not sufficient payment for such a debt. For it is not possible that the blood of bulls and goats could take away sins (Hebrews 10:4). But, the Christ, in his perfection, could die on our behalf, thus purchasing our pardon. In that same chapter, the Hebrew writer noted, And every priest stands ministering daily and offering repeatedly the same sacrifices, which can never take away sins. But this Man, after He had offered one sacrifice for sins forever, sat down at the right hand of God, from that time waiting till His enemies are made His footstool. For by one offering He has perfected forever those who are being sanctified (Hebrews 10:11-15).
And so the entirety of Bible history, from the creation of man, to Gods promises to Abraham, to the sojourn of the children of Israel in Egypt, to the giving of the law on Mount Sinai, to the habitation of the land of Canaan by Israel, to the judgments, captivity and restoration of that nation, to the birth and life of Jesus of Nazareth, all point to the cross, and the subsequent victory over death in Christs resurrection.
God truly has fulfilled his promise in redeeming man from sin, For God so loved the world that He gave His only begotten Son, that whoever believes in Him should not perish but have everlasting life (John 3:16).
The question remains for each of us, what must we do to obtain redemption. While some deny that we must do anything, the question is legitimate, asked by believers, and answered clearly by Peter on Pentecost: