Lord Jesus Christ very often warned against eternal damnation in hell (Mt 5:22; Mt 8:12; Mt 13:42; Mt 18: 8-9; Mt 22:13; Mt 24:51; Mt 25:30; Mk 9: 43-48; Lk 12:52; Jn 5:29).
In the 25th chapter of the Gospel according to St. Matthew has a shocking account of the Last Judgment. Our Divine Savior foretold what He would do and what words He would say to all the damned:
Then shall he say also unto them on the left hand, Depart from me, ye cursed, into the eternal fire which is prepared for the devil and his angels! (Mt 25:41).
This is not one of the possible future versions. This is a foretold event that will take place with absolute certainty in a future that only God knows, for for Him all the moments of time are present in their timeliness (CCC 600).
The exegetes agree that our Lord has foretold exactly what He will do and will say:
When the Son of Man comes in his glory, and all the angels with him, he will sit on his glorious throne. All the nations will be gathered before him, and he will separate the people one from another as a shepherd separates the sheep from the goats. He will put the sheep on his right and the goats on his left (Mt 25: 31-33).
Then He will also say to those on the left hand, ‘Depart from Me, you cursed, into the everlasting fire prepared for the devil and his angels (Mt 25:41).
And they will go away into eternal punishment, but the righteous will go into eternal life (Mt 25:46).
The Catechism of the Catholic Church affirms that Christ the Lord has actually foretold what He will do:
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.612 Jesus solemnly proclaims that he "will send his angels, and they will gather . . . all evil doers, and throw them into the furnace of fire,"613 and that he will pronounce the condemnation: "Depart from me, you cursed, into the eternal fire!" (CCC 1034).
Who knows and understands these words of Christ, but at the same time says that hell is empty and everyone will be saved, insults our Lord Jesus Christ by questioning His truthfulness.
According to the Holy Scriptures and the teaching of the Church, each soul receives an eternal sentence in a particular judgment immediately after death: eternal happiness (very rarely directly, because most often through purgatory) or eternal torment in hell (Lk 16:22; Lk 23:43; 2 Cor 5, 8; Phil 1:23; Heb 9:27; see also Council of Lyons II: DS 857-858; Council of Florence II: DS 1304-1306; Council of Trent: DS 1820; Benedict XII, Const. Benedictus Deus: DS 1000- 1001; John XXII, Bull Ne super his: DS 990; Benedict XII, Const. Benedictus Deus: DS 1002).
At the Last Judgment, this eternal sentence will be publicly confirmed by Christ the Judge for all mankind (Mt 25: 31-46).
The Church teaches in an infallible and dogmatic way from Sacred Scripture that the souls of those who die in a state of mortal sin go forever to Hell after death, where they suffer eternal torment in the fire of hell (Symbol Quicumque: DS 76; Synod of Constantinople : DS 409.411; IV Lateran Council: DS 801; Second Council of Lyons: DS 858; Benedict XII, Const. Benedictus Deus: DS 1002; Council of Florence: DS 1351; Council of Trent: DS 1575; Paul VI, Profession of Faith for the People of God , 12).
...work out your own salvation with fear and trembling (Philippians 2:12).