[quote="traillius, post:1, topic:190377"]
I heard that he described humans and snow-covered dungheaps.
I don't view salvation, mercy, etc, as hiding our sins. I think of it as restoring us to the cleanliness that God originally created Adam and Eve with. In effect, grace and mercy aren't the snow on our dung, Rather they are the cleaning agents wiping the dung off our gold.
I believe he was speaking of justification.
The Catholic understanding is that, when Christians are justified, they become righteous. Insofar that we cooperate with grace, we become righteous. There is change within us. It is for this reason that Catholicism (and Orthodoxy) regard certain Christians as saints. Through ascetic labors and the living of a holy life, they subdued their passions, overcame temptation, and grew in the virtues.
For Lutherans, justification is not so much a change in our nature as a change in God's attitude towards the sinner. A Christian is declared righteous, not made righteous.
Later Protestants would focus on how Christians could live a holy life (e.g. the pietist movement that began in Lutheran churches)