Matt 8:11-12, Matt 13:47-50, Matt 25:46, John 3:18, Rev 20:11-15, and Rev 21:6-8 all clearly state that salvation is not universal. Every knee will bow and every tongue confess, but it will be too late for that to do any good for the unrighteous who did not come to Jesus while they had the chance.
Let's address those verses:
Mat 8:11 And I say unto you, That many shall come from the east and west, and shall sit down with Abraham, and Isaac, and Jacob, in the kingdom of heaven.
Mat 8:12 But the children of the kingdom shall be cast out into outer darkness: there shall be weeping and gnashing of teeth.
In Matthew 8:11-12, we have the time of the return of Christ to usher in the Kingdom. Their will be those that are joined to Christ at His coming (the saints) and the rest are cast out. This time period is DURING the millennial reign. Therefore to suggest that those people that are cast out is like calling the end of the football game at half time. In other words, the Saints are necessary to reign in effort to convert the rest of the congregation (the ones cast out). This is just like it was in the Old Testament. The Levites had to be consecrated BEFORE the rest of the congregation of Israel could be atoned for.
Mat 13:47 Again, the kingdom of heaven is like unto a net, that was cast into the sea, and gathered of every kind:
Mat 13:48 Which, when it was full, they drew to shore, and sat down, and gathered the good into vessels, but cast the bad away.
Mat 13:49 So shall it be at the end of the world: the angels shall come forth, and sever the wicked from among the just,
Mat 13:50 And shall cast them into the furnace of fire: there shall be wailing and gnashing of teeth.
Now those verses are also again during the Millennial reign. Let's talk about that furnace of Fire. That Fire is the tribulation that those people will suffer to remove the dross. Let's Look closer:
Mal_3:2 But who may abide the day of his coming? and who shall stand when he appeareth? for he is like a refiner's fire, and like fullers' soap:
Notice in Malachi that Lord is a refiner's fire? - what does that mean? - well a refiners fire remove the dross of a metal so that what comes out of the fire is the precious pure shimmering beautiful metal. Now what is Fuller's Soap? - well that is the soap used to make a Garment WHITE. You see the Lord is coming with His Saints to make atonement for the rest of the Congregation of Israel (the rest of humanity).
Mat 25:46 And these shall go away into
everlasting punishment: but the righteous into life
eternal.
The verse above uses the Greek word aionios in both sections bold above. The word an adjective describing a point of continuance. (therefore the proper meaning is "age-enduring") and is actually translated like that is some instances depending on Bible version. So this means that some are going to go into punishment (kolasis) that is beyond the age boundary and some will enter into LIFE beyond the age boundary. Now if you know what kolasis is then you will understand that it is the pruning of a tree. Now why do we do that? So that the Tree thrives and doesn't die.
Joh 3:18 He that believeth on him is not condemned: but he that believeth not is condemned already, because he hath not believed in the name of the only begotten Son of God.
That verse above was all statedin the PRESENT tense. You can see that when you look up believeth in a Greek Parsing - πιστευωνG4100 V-PAP-NSM. So that has nothing to do with meaning that someone would always be condemned.
Rev 20:14 And death and hell were cast into the lake of fire. This is the second death.
Rev 20:15 And whosoever was not found written in the book of life was cast into the lake of fire.
Now to the above verses, think back to my earlier comments about the Refiner's fire. You see a lake is where baptism takes place. And the Holy Spirit is likened to Fire as it destroys the old nature within us. You see the carnal person see the fire literally while the Spiritual person understands it spiritually. Consider that John fortold that the Pharisees would be baptized with the Fire of the Holy Spirit:
Mat_3:11 I indeed baptize you with water unto repentance: but he that cometh after me is mightier than I, whose shoes I am not worthy to bear: he shall baptize you with the Holy Ghost, and with fire: (This verse is rendered in other texts as ...'fire of the Holy Spirit').
Rev 21:8 But the fearful, and unbelieving, and the abominable, and murderers, and whoremongers, and sorcerers, and idolaters, and all liars, shall have their part in the lake which burneth with fire and brimstone: which is the second death.
The only thing that destroys death is Life. These that don't receive Life in this dispensation will receive it later through the second death. Yes, the verse is about those people receiving Life through the baptism in the Fire of the Holy Spirit. You see the Spirit is Life:
Joh_6:63 It is the spirit that quickeneth; the flesh profiteth nothing: the words that I speak unto you, they are spirit, and they are life.
I know this subject is tough for many to understand but I hope I have touched on all the verses you referenced. I used to be an adherent to eternal torment and later to annihilationism and then subsequently to Universal Salvation. It was a learning process. But I have studied it deeply and I welcome more verses and questions. Thank you for providing those.