The Son of Man will send his angels, and they will collect out of his kingdom all who cause others to sin and all evildoers. They will throw them into the fiery furnace, where there will be wailing and grinding of teeth. (Mt 31:41-42)

Then he will say to those on his left, ‘Depart from me, you accursed, into the eternal fire prepared for the devil and his angels’. (Mt 25:41)

If anyone says or holds that the punishment of the demons and of impious men is temporary, and that it will have an end at some time, that is to say, there will be a complete restoration of the demons or of impious men, let him be anathema. (Denzinger-Hünermann 411. Synod of Constantinople, confirmed by Pope Vigilius, Canons against Origen, 543 AD)

Jesus often speaks of ‘Gehenna’ of ‘the unquenchable fire’ reserved for those who to the end of their lives refuse to believe and be converted, where both soul and body can be lost (cf. Mt 5:22, 29; 10:28; 13:42, 50; Mk 9:43-48). Jesus solemnly proclaims that he ‘will send his angels, and they will gather . . . all evil doers, and throw them into the furnace of fire’ (Mt 13:41-42), and that he will pronounce the condemnation: ‘Depart from me, you cursed, into the eternal fire!’(Mt 25:41) (Catechism of the Catholic Church, no.  1034)

The teaching of the Church affirms the existence of hell and its eternity. Immediately after death the souls of those who die in a state of mortal sin descend into hell, where they suffer the punishments of hell, ‘eternal fire’ (DS 76; 409; 411; 801; 858; 1002; 1351; 1575; Paul VI, Credo of the People God #12). The chief punishment of hell is eternal separation from God, in whom alone man can possess the life and happiness for which he was created and for which he longs. (Catechism of the Catholic Church, no. 1035)

Hell consists in the eternal damnation of those who die in mortal sin through their own free choice. The principal suffering of hell is eternal separation from God in whom alone we can have the life and happiness for which we were created and for which we long. Christ proclaimed this reality with the words, ‘Depart from me, you cursed, into the eternal fire’ (Mt 25:41). (Compendium of the Catholic Church, 212)

These abodes are not all of the same nature, for among them is that most loathsome and dark prison in which the souls of the damned are tormented with the unclean spirits in eternal and inextinguishable fire. This place is called gehenna, the bottomless pit, and is hell strictly so­called. (Catechism of Trent, no. 1050)

We strive therefore to please God in all things (2Cor 5:9) and we put on the armor of God, that we may be able to stand against the wiles of the devil and resist in the evil day (Eph 6:11-13). Since however we know not the day nor the hour, on Our Lord’s advice we must be constantly vigilant so that, having finished the course of our earthly life, (Heb 9:27) we may merit to enter into the marriage feast with Him and to be numbered among the blessed (Mt 25:31-46) and that we may not be ordered to go into eternal fire (Mt 25:41) like the wicked and slothful servant (Mt 25:26), into the exterior darkness where ‘there will be the weeping and the gnashing of teeth’(Mt 22:13; 25:30). For before we reign with Christ in glory, all of us will be made manifest ‘before the tribunal of Christ, so that each one may receive what he has won through the body, according to his works, whether good or evil’ (2Cor 5:10) and at the end of the world ‘they who have done good shall come forth unto resurrection of life; but those who have done evil unto resurrection of judgment’ (Jn 5:29; Mt 25:46). (Vatican Council II, Dogmatic constitution Lumen gentium, no. 48, November 21, 1964)

God is the infinitely good and merciful Father. But man, called to respond to him freely, can unfortunately choose to reject his love and forgiveness once and for all, thus separating himself for ever from joyful communion with him. It is precisely this tragic situation that Christian doctrine explains when it speaks of eternal damnation or hell. […] In a theological sense however, hell is something else: it is the ultimate consequence of sin itself, which turns against the person who committed it. It is the state of those who definitively reject the Father’s mercy, even at the last moment of their life. (John Paul II. General Audience, July 28, 1999)

[Jesus] claimed judicial power as received from his Father, when the Jews accused him of breaking the Sabbath by the miraculous cure of a sick man. “For neither doth the Father judge any man; but hath given all judgment to the Son.” In this power is included the right of rewarding and punishing all men living, for this right is inseparable from that of judging. Executive power, too, belongs to Christ, for all must obey his commands; none may escape them, nor the sanctions he has imposed. (Pius XI, Encyclical Quas primas, December 11, 1925)

Once restored by the waters of baptism, [the soul] is clothed in luminous whiteness, but with evil actions, it separates from the right path and is stained again. If the fault is grave, the grace of God is lost and one becomes worthy of eternal chastisement. Is there a greater disgrace than this? It is of capital importance for the Christian not to offend God, not to sin, and to keep the soul always in the state of grace. (Pius XII. Letter to the Archbishop of Sucre, August 13, 1954)

The preaching of the first truths of the faith and the final ends of man have not only not lost any of their appropriateness in our times, but have also come to be more necessary and urgent than ever. This includes preaching about hell. There is no doubt that this subject must be spoken of with dignity and wisdom. But, as far as the real substance of this truth goes, the Church has, before God and before men, the sacred duty to proclaim it, to teach it without any mitigation, as Christ has revealed it, and there is no condition of time that might diminish the rigor of this obligation…It is true that the desire for heaven is of itself a more perfect motive than the fear of eternal damnation; but this does not mean that it is for all men also the most efficacious motive, to keep them far from sin and to convert them to God. (Pius XII. Address to Priests and lenten preachers, March 23, 1949)

As apostolic doctrine holds: ‘To them indeed, who according to patience in good works, seek glory and honor and incorruption, eternal life; but to them that are contentious, and who obey not the truth, but give credit to iniquity, wrath and indignation, tribulation and anguish upon every soul of man doing evil’ (Rom 2:7 ff). In the same sense, this same one says elsewhere: ‘In the revelation of the Lord Jesus from heaven with the angels of His power, in a flame of fire, giving vengeance to them who do not know God, and who do not obey the gospel of our Lord Jesus Christ, who shall suffer eternal punishment in destruction . . . when He shall come to be glorified in His Saints, and to be made wonderful in all them who have believed’ (2Thes 1:7 ff). (Denzinger-Hünermann 626. Council of Valence III, On predestination)

 The Church believes that the definitive state of damnation awaits those who die burdened with grave sin (cf. LG 48). It is categorically important to avoid any too close assimilation of the purificatory process which precedes our meeting with God with the process of damnation, as if all that lay between them was the opposition of eternal and temporal: the postmortem purification is ‘straightforwardly other than the pain of damnation’ (Congregation for the Doctrine of the Faith, Recentiores episcoporum Synodi, 7, p. 942.) (International Theological Commission. Some current Questions in Eschatology, no. 8,2. 1990)

For I confess that all men from Adam, even to the consummation of the world, having been born and having died with Adam himself and his wife, who were not born of other parents, but were created, the one from the earth, the other, however, from the rib of the man (cf. Gen 2:7), will then rise again and stand before the Judgment seat of Christ, that every one may receive the proper things of the body, according as he has done, whether it be good or bad (Rom 14:10, 2Cor 5:10); and indeed by the very bountiful grace of God he will present the just, as vessels of mercy prepared beforehand for glory (Rom 9:23), with the rewards of eternal life; namely, they will live without end in the society of the angels without any fear now of their own fall; the wicked, however, remaining by choice of their own with vessels of wrath fit for destruction (Rom 9:22), who either did not know the way of the Lord, or knowing it left it when seized by various transgressions, He will give over by a very just judgment to the punishment of eternal and inextinguishable fire, that they may burn without end. (Denzinger-Hünermann 443. Pelagius I, Letter Humani generis to Childebert I, April, 557)

And every reader of history, or observer of what takes place around him, cannot but know that the rule is for men to end a wicked life by a miserable death, whilst it is the exception for the sinner to die happily; and, on the other hand, it seldom happens that those who live well and holily come to a sad and miserable end, but many good and pious people enter, after their death, into the possession of eternal joys. Those persons are too presumptuous and fool-hardy who, in a matter of such import as eternal felicity or eternal torment, dare to remain in a state of mortal sin even for a day, seeing that they may be surprised by death at any moment, and after death there is no place for repentance, and out of hell there is no redemption. (Saint Robert Bellarmine. The Seven Words on the Cross, Ch. VI)

A learned author says, that the mercy of God sends more souls to hell than his justice; for sinners are induced, by a rash confidence in the divine mercy, to continue in sin, and thus are lost. God is merciful. Who denies it? But great as is his mercy, how many does he send to hell every day? God is merciful: but he is also just; and therefore he is obliged to punish those who offend him. He shows mercy; but to whom? To them who fear him. He hath strengthened His mercy toward them that fear Him. As a father hath compassion on his children, so hath the Lord compassion on them that fear Him (Ps 102:11, 13). (Saint Alphonsus Liguori. Preparation for Death, part III, consideration 23, n. 2)

The saying in flaming fire, deals with both chastising the evil and rewarding the good; but in the chastisement of the evil shows to be bitter, just and everlasting. Then it says, inflicting vengeance, that is, judging the reprobates with flaming fire, reducing to ashes the face of the earth, consuming the damned and casting them down forever. […] This chastisement is everlasting, for they shall suffer the punishment of eternal destruction […] from which it is said that they will be so to say always dying: ‘Death shall be their shepherd’ (Ps 48:15). ‘Their worm shall not die’ (Is 66:24); ‘nor their fire be extinguished.’ (Saint Thomas Aquinas. Commentary on the Second Letter to the Thessalonians, c. 1, lect.2 – 2 Thess1: 6-12 – Spanish)

Picture to yourself a dark city, reeking with the flames of sulphur and brimstone, inhabited by citizens who cannot get forth. Even so the lost are plunged in their infernal abyss; ‒ suffering indescribable torture in every sense and every member; and that because having used their members and senses for sin, it is just that through them they should suffer now. […] Beyond all these sufferings, there is one greater still, the privation and pain of loss of God’s Glory, which is forever denied to their vision. If Absalom cared not to be released from exile, if he might not see his father’s face, how much sorer will it be to be deprived forever of the blessed vision of God? Consider how insupportable the pains of Hell will be by reason of their eternal duration. If the irritating bite of an insect, or the restlessness of fever, makes an ordinary night seem so long and tedious, how terrible will the endless night of eternity be, where nought will be found save despair, blasphemy and fury. (Saint Francis de Sales. Meditation 7 – English)

[Our Lord Jesus Christ] O dearest daughter! I have placed you on the bridge of the doctrine of my truth so that he might serve you, o pilgrims, and administer you the sacraments of the holy Church, but he [a priest] stays in the miserable river below the bridge immersed in the pleasures and miseries of the world. There he exercises his ministry, without noticing the wave that drags him to death and he goes with the devils, his masters, whom he has served and by whom he has been openly guided, along the river. If he does not amend his life, he will be eternally condemned with great reprimand and reproach, that your tongue would be incapable of referring. And he, due to his priestly office, much more than any other lay person. For this reason the same sin is punished more in him than in one who would have stayed in the world. At the moment of death his enemies will accuse him more terribly, as I have told you. (Saint Catherine of Siena. Dialogue, no. 130)

But God, foreknowing all things, prepared fit habitations for both, kindly conferring that light which they desire on those who seek after the light of incorruption, and resort to it; but for the despisers and mockers who avoid and turn themselves away from this light, and who do, as it were, blind themselves, He has prepared darkness suitable to persons who oppose the light, and He has inflicted an appropriate punishment upon those who try to avoid being subject to Him. Submission to God is eternal rest, so that they who shun the light have a place worthy of their flight; and those who fly from eternal rest, have a habitation in accordance with their fleeing. Now, since all good things are with God, they who by their own determination fly from God, do defraud themselves of all good things; and having been [thus] defrauded of all good things with respect to God, they shall consequently fall under the just judgment of God. For those persons who shun rest shall justly incur punishment, and those who avoid the light shall justly dwell in darkness. For as in the case of this temporal light, those who shun it do deliver themselves over to darkness, so that they do themselves become the cause to themselves that they are destitute of light, and do inhabit darkness; and, as I have already observed, the light is not the cause of such an [unhappy] condition of existence to them; so those who fly from the eternal light of God, which contains in itself all good things, are themselves the cause to themselves of their inhabiting eternal darkness, destitute of all good things, having become to themselves the cause of [their consignment to] an abode of that nature. (Saint Irenaeus of Lyons. Against Heresies, IV, 39, 4)