Let's look at the doctrine of justification. Dr. John Ankerberg and Dr. John Weldon have this to say in an article
What Does the Roman Catholic Church Teach About the Doctrine of Justification?: "...In essence, the Reformed Protestant position is that a person, once justified, can never lose that justification. Why? Because the justification depends solely upon Christ’s merits and not anything in themselves.
"But this is the very reason why Rome teaches that a person’s justification is not secure. Because it does depend upon what a person does, it may, in fact, be lost by what a person fails to do. Catholicism, therefore, teaches that the commission of mortal sin causes the person’s justification to be cancelled or lost. Thus, once a person’s justification is lost, the sacrament of penance, which involves confession, absolution and satisfaction, must be undertaken in order to restore justification."
From the Catholic Council of Trent:
Thus, in the section "Canons Concerning Justification," we read e.g.:
Canon 9: 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… let him be anathema.
Canon 11: 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 [i.e., the Catholic view of infused justification], or also that the grace by which we are justified is only the good will of God, let him be anathema.
Canon 12: If anyone says that justifying faith is nothing more 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.
Not surprisingly, Trent also decreed that good works increase our justification. For example:
Canon 24: If anyone says that the justice received [i.e., justification] is not preserved and also not increased before God through good works, but that those works are merely the fruits and signs of justification obtained, but not the cause of its increase, let him be anathema.
The Council closed with:
Canon 33: If anyone says that the Catholic doctrine of justification as set forth by the Holy Council and the present decree, derogates in some respect from the glory of God or the merits of our Lord Jesus Christ... let him be anathema.
Ankerberg Theological Research Institute articles on Roman Catholicism