Here is a little help to get a head start on our future discussions on assurance of salvation. It is often either forgotten or unknown today that the doctrine of assurance was at the very heart of the divide between Protestants and Catholics during the Reformation. Here are two standard quotes from the Catholic viewpoint. The first comes from the Council of Trent, which was designed specifically to counter Luther and Calvin and the teaching of Protestants, and the second comes from a major Catholic theologian who was a contemporary of Calvin's. Both quotes accurately convey what is still Catholic teaching today.
“But, although it is necessary to believe that sins neither are remitted, nor ever were remitted save gratuitously by the mercy of God for Christ's sake; yet is it not to be said, that sins are forgiven, or have been forgiven, to any one who boasts of his confidence and certainty of the remission of his sins, and rests on that alone; seeing that it may exist, yea does in our day exist, amongst heretics and schismatics; and with great vehemence is this vain confidence, and one alien from all godliness, preached up in opposition to the Catholic Church. But neither is this to be asserted,-that they who are truly justified must needs, without any doubting whatever, settle within themselves that they are justified, and that no one is absolved from sins and justified, but he that believes for certain that he is absolved and justified; and that absolution and justification are effected by this faith alone: as though whoso has not this belief, doubts of the promises of God, and of the efficacy of the death and resurrection of Christ. For even as no pious person ought to doubt of the mercy of God, of the merit of Christ, and of the virtue and efficacy of the sacraments, even so each one, when he regards himself, and his own weakness and indisposition, may have fear and apprehension touching his own grace; seeing that no one can know with a certainty of faith, which cannot be subject to error, that he has obtained the grace of God.”
(Council of Trent, sixth session, §9, “Against the Vain Confidence of Heretics”)
“The principle heresy of Protestants is that saints may obtain to a certain assurance of their gracious and pardoned state before God.” (Cardinal Robert Bellarmine, 1542-1621)