Just to add, the most famous sermon on this topic is probably that of St. Leonard of Port Maurice. First he says: “Pious souls, you may leave; this sermon is not for you. Its sole purpose is to contain the pride of libertines who cast the holy fear of God out of their heart and join forces with the devil who, according to the sentiment of Eusebius, damns souls by reassuring them.” All such sentiments from other saints have the same purpose.
At the end, he shows the principle I stated in my prior post:
Brothers, I want to send all of you away comforted today. So if you ask me my sentiment on the number of those who are saved, here it is: Whether there are many or few that are saved, I say that whoever wants to be saved, will be saved; and that no one can be damned if he does not want to be. And if it is true that few are saved, it is because there are few who live well. As for the rest, compare these two opinions: the first one states that the greater number of Catholics are condemned; the second one, on the contrary, pretends that the greater number of Catholics are saved. Imagine an Angel sent by God to confirm the first opinion, coming to tell you that not only are most Catholics damned, but that of all this assembly present here, one alone will be saved. If you obey the Commandments of God, if you detest the corruption of this world, if you embrace the Cross of Jesus Christ in a spirit of penance, you will be that one alone who is saved.
Now imagine the same Angel returning to you and confirming the second opinion. He tells you that not only are the greater portion of Catholics saved, but that out of all this gathering, one alone will be damned and all the others saved. If after that, you continue your usuries, your vengeances, your criminal deeds, your impurities, then you will be that one alone who is damned.
What is the use of knowing whether few or many are saved? Saint Peter says to us, “Strive by good works to make your election sure.” When Saint Thomas Aquinas’s sister asked him what she must do to go to heaven, he said, “You will be saved if you want to be.” I say the same thing to you, and here is proof of my declaration. No one is damned unless he commits mortal sin: that is of faith. And no one commits mortal sin unless he wants to: that is an undeniable theological proposition. Therefore, no one goes to hell unless he wants to; the consequence is obvious. Does that not suffice to comfort you? Weep over past sins, make a good confession, sin no more in the future, and you will all be saved. Why torment yourself so? For it is certain that you have to commit mortal sin to go to hell, and that to commit mortal sin you must want to, and that consequently no one goes to hell unless he wants to. That is not just an opinion, it is an undeniable and very comforting truth; may God give you to understand it, and may He bless you. Amen.