Would you be so kind as to link some of that here, if it available online? I am sure many would find it useful.
"Broad is the way that leads to destruction, and many there are who go in that way" (Mt7.13).
Hell has then different gates, but these gates stand on our earth. "Her gates are sunk into the ground." (Lam 2.9) These are the vices by which men offend God, and
draw down upon themselves chastisements and eternal death. Among the other vices, there are four which send most souls to Hell, and on this earth bring upon men the
scourges of God; and these four are, HATRED, BLASPHEMY, THEFT, and IMPURITY.
Behold, the four gates by which the greater number of souls enter Hell; and it is of these four that I mean to speak today, in order that you may amend and cure yourselves of these four vices, otherwise God will cure you of them, but by your own destruction.
1. Hell's Widest Gate: Impurity
We have now to speak of the fourth gate of Hell, which is impurity [sexual sins], and it is by this gate that the greater number of the damned enter. Some will say that it is a trifling sin. Is it a trifling sin? It is a mortal sin. St. Antoninus writes that such is the nauseousness of this sin that the devils themselves cannot endure it.
Moreover, the Doctors of the Church say that certain demons, who have been superior to the rest, remembering their ancient dignity, disdain tempting to so loathsome a sin. Consider then how disgusting he must be to God, who, like a dog, is ever returning to his vomit, or wallowing like a pig in the stinking mire of this accursed vice (2 Pet 2.22).
The impure say, moreover, "God has compassion on us who are subject to this vice, because He knows that we are flesh." What do you say? God has compassion on this vice? But you must know that the most horrible chastisements with which God has ever visited the earth have been drawn down by this vice. St. Jerome says that this is the only sin of which we read that it caused God to repent of having made man, for all flesh had become corrupted (Gen 6.6-12). And so it is, St. Jerome says, that there is no sin which God punishes so rigorously, even upon earth, as this. He once sent fire from Heaven upon five cities, and consumed all their inhabitants for this sin (Sodom and Gomorrah,
Principally on account of this sin did God destroy mankind, with the exception of eight persons, by the flood. It is a sin which God punishes, not only in the other life, but in this also. Because, says God, you have forgotten Me and turned your back upon Me, for a miserable pleasure of the flesh, I am resolved that even in this life you shall pay the price of your wickedness (Ezek 23.35). You say, "God has compassion upon men subject to this sin." But it is this sin that sends most men to Hell. St. Remigius says that the greater number of the damned are in Hell through this vice. Father Segneri writes that as this vice fills the world with sinners, so it fills Hell with damned souls; and before him St. Bernardine of Siena wrote: "This sin draws the whole world, as it were, into sin." And before him St. Bernard and St. Isidore said that "the human race is brought under the power of the devil more by lust than by all the other vices." The reason is because this vice proceeds from the natural inclination of the flesh. Hence St Thomas Aquinas says that the devil does not take such complacency in securing the commission of any other sin as of this, because the person who is plunged in this infernal mire remains lodged therein, and almost wholly unable to free himself again. "No one is so obstinate in sin as the impure," says St. Thomas of Villanova. Moreover, this vice deprives one of all light, for the impure man becomes so blind as almost wholly to forget God, says St. Laurence Justinian; which is in accordance with what is said by the prophet Hosea: They will not set their thoughts to return to their God; for the spirit of fornication is in the midst of them, and they have not known God (Hos 5.4).
The impure man does not know God; he obeys neither God nor reason, as St. Jerome says; he obeys only the sensual appetite which causes him to act like a beast. This sin, because it flatters, makes us fall at once into the habit of it, a habit which some carry with them even to death. You see husbands, and decrepit old men, indulge in the same thoughts and committing the same sins that they committed in their youth. And because sins of this kind are so easily committed, they become multiplied without number. Ask of the sinner how many impure thoughts he has consented to: he will tell you he cannot remember. But, brother, if you cannot tell the number, God can; and you know that a single willful immodest thought is enough to send you to Hell. How many immodest words have you spoken, in which you took delight yourself, and by which you scandalized your neighbour? From thoughts and words you proceed to acts, and to those innumerable impurities which those wretches roll and wallow in like swine, without ever being satisfied, for this vice is never satisfied.
But, Father, you will say, how can I hold out against the innumerable temptations which assail me? I am weak, I am flesh. And since you are weak, why not recommend yourself to God, and to most holy Mary, who is the mother of purity? Since you are flesh, why do you throw yourself in the way of sin? Why do you not guard your eyes? Why do you gaze upon those objects from which temptations flow?...It is to be remarked, moreover, that this sin brings with it innumerable others: enmities, thefts, and, more especially, sacrilegious confessions and Communions, by reason of the shame which will not allow these impurities to be disclosed in confession. And let us remark here in passing, that it is sacrilege above all things that brings upon us sickness and death; for, says the Apostle, "He that eats and drinks unworthily, eats and drinks judgement to himself, not discerning the body of the Lord"; and then he adds: "therefore are many infirm and weak among you." (1 Cor 11.29-30)
And St. John Chrysostom, in explanation of that passage, says that St. Paul speaks of persons who were chastised with bodily infirmities because they received the Sacrament with a guilty conscience. My brethren, should you ever have been sunk in this vice, I do not bid you be disheartened, but arise at once from this foul and infernal pit; beg of God immediately to give you light, and stretch out His hand to you. The first thing that you have to do is to break with the occasion of sin: without that, preaching and tears and resolutions and confessions, all are lost. Remove the occasions, and then constantly recommend yourself to God, and to Mary the mother of purity. No matter how grievously you may be tempted, do not be discouraged by the temptation; at once call to your aid Jesus and Mary, pronouncing their sacred names. These blessed names have the power of making the devil fly, and stifling that hellish flame within you. If the devil persists in tempting you, persevere in calling upon Jesus and Mary, and certainly you shall not fall. In order to rid yourself of your evil habits, undertake some special devotion to our Lady; begin to fast in her honour upon Saturdays; contrive to visit her image every day, and beg of her to obtain for you deliverance from that vice. Every morning immediately after rising, never omit saying three "Hail Marys" in honour of her purity and do the same when going to bed;* and above all things, as I have said, when the temptation is most troublesome, call quickly upon Jesus and Mary. Beware, brother, if you do not be converted now, you may never be converted.
Scroll down to find more readings: http://www.basilica.org/pages/ebooks/St.%20Alphonsus%20Liguori-Natural%20Calamities_Divine%20Threats_Four%20Gates%20of%20Hell.html
For St. Alphonsus, the four Gates of Hell are Hatred, Blasphemy, Theft, and Impurity.