Christians should care because it is ultimately a matter of life and death. Others should care because it's a doctrine that defines – or at least should define – the core belief of 600 million people globally, shaping how they engage with the world around them. As justification goes, so goes the church. A muddied view of justification could muddy the Protestant fountainhead, limiting its effort to quench the thirst for acceptance that we all feel deep down.
For Martin Luther, the father of the Reformation, justification was an intensely personal question. As a monk and devout Catholic, Luther had tried everything to assuage his guilt and get right with God. But he was still tormented by feelings of unworthiness and terrified by God's righteous wrath.
Until he understood that the righteous shall live by faith (Rom. 1:16-17).
Like millions of Christians after him, Luther took solace in the good news that if we believe in Jesus Christ, God will count our faith as righteousness. We are not declared innocent and righteous in God's sight by works, not even by our best moral efforts. We are justified by faith alone.
Of all the points of contention between the early Reformers and the Catholic Church, disagreement over justification was sharpest. Luther himself said that it was "the doctrine by which the Church stands or falls." The crux of the debate was this: What, if any, role do our own actions play in being justified?
The Reformers saw in the Bible that we are justified by faith alone. The Catholic Church has always acknowledged that the Christian was saved by faith; it was the alone part Catholics questioned. Do not works play some role in our justification? they asked.
Of course, Protestants insist on good works, too. But these works serve as corroborating evidence, not as any ground for our justification. Indeed, that's what the controversial second chapter of the New Testament book of James is saying: Works are how we "see" in others the kind of genuine faith that underlies justification. The gospel says, "believe on the Lord Jesus Christ and you shall be saved," not "believe on the Lord Jesus Christ and cooperate with transforming grace and you shall be saved." Yet the 16th century Council of Trent condemns those who believe in justification by faith alone.