Two Radically Different Views of Salvation
11 The justification of man
We are accounted righteous before God solely on account of the merit of our Lord and Savior Jesus Christ through faith and not on account of our own good works or of what we deserve. Consequently, the teaching that we are justified by faith alone is a most wholesome and comforting doctrine. This is taught more fully in the homily on Justification.
12 Good works
Although good works, which are the fruits of faith and follow on after justification, can never atone for our sins or face the strict justice of God's judgment, they are nevertheless pleasing and acceptable to God in Christ and necessarily spring from a true and living faith. Thus a living faith is as plainly known by its good works as a tree is known by its fruit.
13 Works before justification
Works done before receiving the grace of Christ and the inspiration of his Spirit are not pleasing to God. This is because they do not spring out of faith in Jesus Christ. Nor do they make people fit to receive grace or (as the schoolmen say) to deserve grace of congruity. On the contrary, because they are not done as God has willed and commanded that they should be done, it is undoubtedly the case that they have the nature of sin.
The Council of Trent
Chapter 7: The Causes of this justification are:
For though no one can be just except he to whom the merits of the passion of our Lord Jesus Christ are communicated, yet this takes place in that justification of the sinner, when by the merit of the most holy passion, the charity of God is poured forth by the Holy Ghost in the hearts of those who are justified and inheres in them; whence man through Jesus Christ, in whom he is ingrafted, receives in that justification, together with the remission of sins, all these infused at the same time, namely, faith, hope and charity.
Session 6, Canons 9, 11, 12
If anyone says that the sinner is justified by faith alone, meaning that nothing else is required to cooperate in order to obtain the grace of justification, and that it is not in any way necessary that he be prepared and disposed by the action of his own will, let him be anathema.
If anyone says that men are justified either by the sole imputation of the justice of Christ or by the sole remission of sins, to the exclusion of the grace and the charity which is poured forth in their hearts by the Holy Ghost, and remains in them, or also that the grace by which we are justified is only the good will of God, let him be anathema.
If anyone says that justifying faith is nothing else than confidence in divine mercy, which remits sins for Christ's sake, or that it is this confidence alone that justifies us, let him be anathema.
"The fundamental difference was this. Trent said that God does not justify anyone until real righteousness inheres within the person. In other words, God does not declare a person righteous unless he or she is righteous. So, according to Roman Catholic doctrine, justification depends on a person’s sanctification. By contrast, the Reformers said justification is based on the imputation of the righteousness of Jesus. The only ground by which a person can be saved is Jesus’ righteousness, which is reckoned to him when he believes.
There were radically different views of salvation. They could not be reconciled. One of them was the gospel. One of them was not. Thus, what was at stake in the Reformation was the gospel of Jesus Christ." ~R.C. Sproul, What Does the Roman Catholic Church Believe About Justification?