Justification, God's act of declaring a sinner righteous by faith alone, is the center of the Christian faith. Martin Luther wrote in the Smalcald Articles:
The first and chief article is this: Jesus Christ, our God and Lord, died for our sins and was raised again for our justification (Romans 3:24-25). He alone is the Lamb of God who takes away the sins of the world (John 1:29), and God has laid on Him the iniquity of us all (Isaiah 53:6). All have sinned and are justified freely, without their own works and merits, by His grace, through the redemption that is in Christ Jesus, in His blood (Romans 3:23-25). This is necessary to believe. This cannot be otherwise acquired or grasped by any work, law, or merit. Therefore, it is clear and certain that this faith alone justifies us... Nothing of this article can be yielded or surrendered, even though heaven and earth and everything else falls (Mark 13:31).
Calvin, in the Institutes, says that we are justified in our union with Christ:
I acknowledge that we are devoid of this incomparable gift until Christ become ours. Therefore, to that union of the head and members, the residence of Christ in our hearts, in fine, the mystical union, we assign the highest rank, Christ when he becomes ours making us partners with him in the gifts with which he was endued. Hence we do not view him as at a distance and without us, but as we have put him on, and been ingrafted into his body, he deigns to make us one with himself, and, therefore, we glory in having a fellowship of righteousness with him. (Book III, Chapter 11).
This is genuinely an astonishing invitation. There is nothing we can do to be in union with God. No work, no law, no merit will get us there...just faith in the work of Christ on our behalf and our mystical union with Christ.
This is so different from other religions. In Buddhism Enlightenment is no free gift but the result of personal discipline and the hard work of meditation and the eight-fold path.
I think the misunderstanding of Justification (and its implications) stands at the heart of the Religious Right's holy war against LGBT people. By protecting "family values" they are uplifting works, law and merit as the standards of their goodness and godliness. They are establishing a culture of law and misunderstanding their own wickedness (eek I sound like Calvin). Justification by faith says that there is absolutely nothing you can lift up to make you righteous before God. NOTHING.
This is so radical when you think about it.