Redemption is at the heart of the Gospel, it is the "good news" and can only be understood if the fallen nature of man and original sin is also understood. Redemption can only be understood if the need for redemption is also understood. Man is seperated from God by sin and sin has to be punished if the justice inherant in the very nature of God is to be satisfied. Man had a way to please God through the covenant of works but as no man is without sin this path to God is impossible, the law serves to condemn man and show his need for redemption but cannot save him.
Jesus Christ was unique in that he was born without original sin, not only that, he also lived a sinless life. Jesus was not subject to death and he did not deserve to die. By willingly giving up his life and experiencing the death he did not deserve he paid the price for sin. By having faith in Christ we as humans are able to partake in his righteousness and we are justified through the punishment that Christ suffered and by the perfect life that Christ lead. Having faith in Christ is impossible for fallen man as he is totally separated from God and unable to even comprehend what faith is. Man is not sick with sin, man is dead in sin.
Faith is different to belief, the devils believe in Jesus and they tremble. Faith is a gift from God which he grants to his elect entirely according to his own will, according to his will he regenerates his chosen people, enabling those people to have faith and to enter into a relationship with God. We are not saved by faith, we are saved by the death of Jesus Christ who we approach in faith as a result of being regenerated by God.
The reformed distinctive is that regeneration proceeds faith and such regeneration is wholly the prerogative of God, we do not choose to become a friend of God, it is God who chooses to become our father and friend. By regeneration we acquire a new nature that enables us to please God and this nature is in conflict with our fallen human nature. Throughout our life this constant battle will lead to increasing levels of sanctification as our new nature opens our eyes to sin and gives us a desire to please God. Only when he leave our fallen nature behind in death will we achieve the glorious state of sinless perfection where our only desire will be to worship God.