Quotable: From the Most Recent White Horse Inn, Mark Noll

On the differences between the Reformed view of justification and what the Catholic Catechism says:

I actually think that what's happening there is that Catholics use one word for what Protestants have over the last 4 and 5 centuries talked about in terms of justification and sanctification (response from Michael Horton, "but we never mention merit"). Allister McGrath has written some very sharp writings on the developments in the Catholic church. He has made very clear that some confusion between Catholics and Protestants is due to the fact that Catholics use the term justification for the entire process of salvation that classic protestants divide up into phases defined by justification and sanctification."

Mark Noll

From my own view, I think the difference concerns the nature of imputation (external vs. internal). I don't know if Noll is being true to either Catholic or Protestant views by saying the most important part is that both sides are "Augustinian."

See Ludwig Ott in Fundamentals of Catholic Dogma, pg. 250:

The point of departure of Luther’s doctrine of Justification is the conviction that human nature was completely corrupted by Adam’s sin, and that original sin consists formally in evil concupiscence. Luther conceives Justification as a juridicial act (actus forensis) by which God declares the sinner to be justified, although he remains intrinsically unjust and sinful. On the negative side, Justification is not a real eradication of sin, but merely a non-imputation or covering of sin. On the positive side it is not an inner renewal and sactification, but merely an external imputation of Christ’s justice. The subjective condition of Justification is fiducial faith, that is, the confidence of man, which is associated with the certainty of salvation, that the merciful God will forgive him his sins for Christ’s sake.”
...
The Council of Trent, referring to Col. I, 13, defined Justification as: ‘translation from that condition in which man is born as the son of the first Adam into the state of grace and adoption among the children of God through the second Adam, Jesus Christ, our Savior’…on the negative side it is a true eradication of sin; on the positive side it is a supernatural sanctifying and renewal of the inner man…The Reformers’ teaching of the merely external imputation of Christ’s justice was rejected, by the Council of Trent, as heretical.