There is no list of which sins are forgiven and which ones are not. Christ died for ALL of our sins. Thank you, Lord.
No doubt, except for blaspheming the Holy Spirit.
No doubt. Yet St. Alphhonsus is not claiming otherwise. His premise is that the sins of impurity are responsible for sending more people to Hell than any other sin. He quotes others as saying that they believe, in fact, that sins of impurity send more people to Hell than all other sins combined. This is not, however, in any way to imply that such sins are the only ones that are important enough to eradicate in our lives.
It is therefore something of a mental misdirection to suppose that St. Alphonsus' words are to be dismissed because they don't encompass the obvious fact that "there are other sins, too, you know." Yes, we all know this. So did he. Yet his observations, written in the 1700's, BTW, certainly should give us all some pause in our own age of accelerated and ubiquitous sexual license and perversity. Why dismiss his counsel out-of-hand because he did not include other sins that were extraneous to his point?
If it is true that the predominant reason people wind-up in Hell is a misuse of the sexual faculties - and that is certainly a reasonable supposition, especially these days - then it would be in our interest to take this counsel seriously. Even if the number landing in Hell over this set of sins is not as great as St. Alphonsus alleges, it is undoubtedly the case that many souls do wind-up in Hell over these things, just the same. St. Alphonsus is speaking especially to us in our own day here, and his words should be reflected on by all of us. Many Christians are self-deluded in these matters, without a doubt.