The iMonk has a good post on the Reformation and a lengthy quote from Martin Luther's Concerning Christian Liberty (1520).
But you will ask:—“What is this word, and by what means is it to be used, since there are so many words of God?” I answer, the Apostle Paul (Rom. i.) explains what it is, namely, the Gospel of God, concerning His Son, incarnate, suffering, risen, and glorified through the Spirit, the sanctifier. To preach Christ is to feed the soul, to justify it, to set it free, and to save it, if it believes the preaching. For faith alone, and the efficacious use of the word of God, bring salvation.Chris Castaldo retells the story of Luther at the Diet of Worms in 1521. He concludes with this quote from McGrath's Christianity's Dangerous Idea:
At its heart, the emergence and growth of Protestantism concerned one of the most fundamental questions that can confront any religion: Who has the authority to define its faith? Institutions or individuals? Who has the right to interpret its foundational document, the Bible?While Tetzel's selling of indulgences were the primary problem dealt with in 1517 these posts capture the major issues of the Reformation - what is the Gospel and who has the authority to interpret Scripture? For more on the latter see this post.
Update: Found another post on John Armstrong's blog. He examines Peter Kreeft’s book The God Who Loves You in light of the Reformation:
His seventh big idea brought Dr. Kreeft back to the Protestant Reformation and made him think about its core message. On this day I find his insight powerful and unifying. His seventh “eureka” moment led him to write: “The gift of God’s love is ours for the taking.” He writes:I have not read Kreeft's book (though I have examined some of his series on philosophy (Socrates meets...), but from these excerpts he certainly understood the important principle sola fide!
I am a Roman Catholic. But the most liberating idea I have ever learned I heard first from Martin Luther. Pope John Paul II told the German Lutheran bishops that Luther was profoundly right about this idea. He said that Catholic teaching affirms it just as strongly and that there is no contradiction between Protestant and Catholic theology on this terribly important point, which was the central issue of the Protestant Reformation. I speak, of course, about “justification by faith” and its consequence, which Luther called “Christian liberty” or “the liberty of a Christian” in his little gem of fan essay by that name (The God Who Loves You, 23).
The point, Kreeft reasons, is rather simple: heaven is free because God’s love is free! Salvation is a gift to be taken by faith and not by human performance in any sense.