Council of Trent, Session VI, Chap. 9.
Against the Vain Confidence of Heretics
Although it is necessary to believe that sins are neither forgiven, nor ever have been forgiven, except gratuitously by divine mercy for Christ’s sake, yet it must not be said that sins are forgiven or have been forgiven to anyone who boasts of his confidence and certainty of the forgiveness of his sins and rests on that alone, since among heretics and schismatics this vain confidence, remote from all piety [can. 12], may exist, indeed in our own troubled times does exist, and is preached against the Catholic Church with vigorous opposition. But neither is this to be asserted, that they who are truly justified without any doubt whatever should decide for themselves that they are justified, and that no one is absolved from sins and is justified, except him who believes with certainty that he is absolved and justified, and that by this faith alone are absolution and justification effected [can. 14], as if he who does not believe this is doubtful of the promises of God and of the efficacy of the death and resurrection of Christ. For, just as no pious person should doubt the mercy of God, the merit of Christ, and the virtue and efficacy of the sacraments, so every one, when he considers himself and his own weakness and indisposition, may entertain fear and apprehension as to his own grace [can. 13], since no one can know with the certainty of faith, which cannot be subject to error, that he has obtained the grace of God.
Canons On Justification
Can. 12. If anyone shall say that justifying faith is nothing else than confidence in the divine mercy which remits sins for Christ’s sake, or that it is this confidence alone by which we are justified: let him be anathema.
Can. 13. If anyone shall say that it is necessary for every man in order to obtain the remission of sins to believe for certain and without any hesitation due to his own weakness and indisposition that his sins are forgiven him: let him be anathema.
Can. 14. If anyone shall say that man is absolved from his sins and justified, because he believes for certain that he is absolved and justified, or that no one is truly justified but he who believes himself justified, and that by this faith alone absolution and justification are perfected: let him be anathema.