All who die in mortal sin will go to Hell?

Pope Eugene IV, Council of Florence, “Letentur coeli,” Sess. 6, July 6, 1439, ex cathedra: “We define also that… the souls of those who depart this life in actual mortal sin, or in original sin alone, go straightaway to Hell, but to undergo punishments of different kinds.”

Catholics must also know that all who die in mortal sin will go to Hell forever. Mortal sins include: murder, fornication (i.e. sexual acts outside of marriage or acts leading up to sex outside of marriage), lying, drunkenness, consenting to impure thoughts, masturbation, looking at pornography, adultery, cheating, taking God’s name in vain, birth control (NFP) or artificial contraception, assisting the propagation of heresy, funding heretics, dishonoring the Sabbath, breaking the commandments, etc. If someone were to commit a mortal sin and then go to Confession, he must have the firm resolution never to commit the sin again. This is called the firm purpose of amendment. If a person commits a mortal sin and doesn’t have the firm purpose of amendment when he goes to Confession, he commits a sacrilege and the Confession is invalid. Most souls go to Hell because of sins of the flesh. Those who are committing sins of the flesh need to stop immediately if they don’t want to perish forever in the fires of Hell.

St. Alphonsus on the damnation of the impure: "Continue, O fool, says St. Peter Damian (speaking to the unchaste), continue to gratify the flesh; for the day will come in which thy impurities will become as pitch in thy entrails, to increase and aggravate the torments of the flame which will burn thee in Hell: 'The day will come, yea rather the night, when thy lust shall be turned into pitch, to feed in thy bowels the everlasting fire." (Preparation for Death, abridged version, p. 117)