The only one who can answer your question is God himself, since he alone knows his reasons for creating things and why they must end as they do.
That being said we do have some guidance about this in the Bible.
All Scripture is quoted from the King James translation, unless otherwise noted.
As a lifelong Southern Baptist I can pass on to you what I have been taught over the years, and give you the references I have from the Bible itself.
- The lake of fire is a place of eternal torment:
Revelation 20:10 And the devil that deceived them was cast into the lake of fire and brimstone, where the beast and the false prophet are, and shall be tormented day and night for ever and ever.
The lake of fire was apparently created as a place for the eternal torture of Satan and the rebellious Angels, the reason for believing that is lies in the fact that:
Revelation 19:19 through 21 And I saw the beast, and the kings of the earth, and their armies, gathered together to make war against him that sat on the horse, and against his army. 20 And the beast was taken, and with him the false prophet that wrought miracles before him, with which he deceived them that had received the mark of the beast, and them that worshipped his image. These both were cast alive into a lake of fire burning with brimstone. 21 And the remnant were slain with the sword of him that sat upon the horse, which sword proceeded out of his mouth: and all the fowls were filled with their flesh.
It should be noted that:
And the beast was taken, and with him the false prophet
These both were cast alive into a lake of fire burning with brimstone.
the remnant were slain with the sword of him that sat upon the horse,
The beast, the false prophet, and the Devil are all cast into the lake of fire immediately; since they were judged at the cross when Jesus paid for our sins.
But let's look at point number 3 which what has to do with us. That says that the remnant of the Army at Armageddon were slain and their Earthly bodies were eaten by the fowls of the air, in consonance with:
Revelation 19:17 and 18 And I saw an angel standing in the sun; and he cried with a loud voice, saying to all the fowls that fly in the midst of heaven, Come and gather yourselves together unto the supper of the great God; 18 That ye may eat the flesh of kings, and the flesh of captains, and the flesh of mighty men, and the flesh of horses, and of them that sit on them, and the flesh of all men, both free and bond, both small and great.
So that is the disposition of Satan the Rebellious Angels and the Earthly bodies of man. and that is in accordance with:
Genesis 3:19 In the sweat of thy face shalt thou eat bread, till thou return unto the ground; for out of it wast thou taken: for dust thou art, and unto dust shalt thou return.
but then we have:
Revelation 20:11 through 13 And I saw a great white throne, and him that sat on it, from whose face the earth and the heaven fled away; and there was found no place for them. 12 And I saw the dead, small and great, stand before God; and the books were opened: and another book was opened, which is the book of life: and the dead were judged out of those things which were written in the books, according to their works. 13 And the sea gave up the dead which were in it; and death and hell delivered up the dead which were in them: and they were judged every man according to their works.
So if the Earthly bodies have returned to dust, then who are these dead I saw the dead, small and great, stand before God;
Our first clue to identifying these comes from:
Genesis 2:7 And the LORD God formed man of the dust of the ground, and breathed into his nostrils the breath of life; and man became a living soul.
Our second clue comes from:
Matthew 10:28 And fear not them which kill the body, but are not able to kill the soul: but rather fear him which is able to destroy both soul and body in hell.
According to the words of Jesus; the body can suffer death, but only God can kill both body and soul in Hell!
However we have already determined that the earthly body will return to dust, and the dust is a part of the Earth, so then how can it be destroyed in Hell along with the Soul?
The answer to that is not so easy to determine, but lets see what we can find in the Bible to help untangle this mystery.
1st Thessalonians 4:13 through 17 But I would not have you to be ignorant, brethren, concerning them which are asleep, that ye sorrow not, even as others which have no hope. 14 For if we believe that Jesus died and rose again, even so them also which sleep in Jesus will God bring with him. 15 For this we say unto you by the word of the Lord, that we which are alive and remain unto the coming of the Lord shall not prevent them which are asleep. 16 For the Lord himself shall descend from heaven with a shout, with the voice of the archangel, and with the trump of God: and the dead in Christ shall rise first: 17 Then we which are alive and remain shall be caught up together with them in the clouds, to meet the Lord in the air: and so shall we ever be with the Lord.
So now we have a conundrum, in that Paul says; For if we believe that Jesus died and rose again, even so them also which sleep in Jesus will God bring with him. and later on in that same statement he says; the dead in Christ shall rise first: 17 Then we which are alive and remain shall be caught up together with them in the clouds, to meet the Lord in the air: and so shall we ever be with the Lord.
Unless I am misreading this first he is bringing back the dead with him and in the second statement they are rising up to meet him in the air. How is this possible?
It is only possible if that refers to two different people or rather two different eternal beings. These would appear to be the Soul which returns with Jesus and the resurrection body which we inherit at that time, since the last verse says we who are still alive will also be caught up. That cannot refer to our earthly bodies since God has decreed that they must return to dust.
So now lets tackle that part about the unsaved being tortured forever in the lake of fire, and incidentally it is not eternity in Hell, since:
Revelation 20:14 And death and hell were cast into the lake of fire. This is the second death.
Hell is a temporary holding place for the unsaved dead, awaiting the great white throne judgment. We know this because Jesus told the thief on the cross next to him:
Luke 23:43 And Jesus said unto him, Verily I say unto thee, To day shalt thou be with me in paradise.
So those that are saved will be with Jesus the same day we die our physical death. and if we go back to 1st Thessalonians 4:16 if we die before Jesus second coming our souls get to return with him to get our resurrection bodies.
So lets determine if we can learn who exactly the saved refers to:
Matthew 10:16 through 22 Behold, I send you forth as sheep in the midst of wolves: be ye therefore wise as serpents, and harmless as doves. 17 But beware of men: for they will deliver you up to the councils, and they will scourge you in their synagogues; 18 And ye shall be brought before governors and kings for my sake, for a testimony against them and the Gentiles. 19 But when they deliver you up, take no thought how or what ye shall speak: for it shall be given you in that same hour what ye shall speak. 20 For it is not ye that speak, but the Spirit of your Father which speaketh in you. 21 And the brother shall deliver up the brother to death, and the father the child: and the children shall rise up against their parents, and cause them to be put to death. 22 And ye shall be hated of all men for my name's sake: but he that endureth to the end shall be saved.
So this is the how we get saved, but still who is evasive, since Jesus is saying that only the ones who endure to the end will be saved. So consider:
Matthew 19:23 through 30 Then said Jesus unto his disciples, Verily I say unto you, That a rich man shall hardly enter into the kingdom of heaven. 24 And again I say unto you, It is easier for a camel to go through the eye of a needle, than for a rich man to enter into the kingdom of God. 25 When his disciples heard it, they were exceedingly amazed, saying, Who then can be saved? 26 But Jesus beheld them, and said unto them, With men this is impossible; but with God all things are possible. 27 Then answered Peter and said unto him, Behold, we have forsaken all, and followed thee; what shall we have therefore? 28 And Jesus said unto them, Verily I say unto you, That ye which have followed me, in the regeneration when the Son of man shall sit in the throne of his glory, ye also shall sit upon twelve thrones, judging the twelve tribes of Israel. 29 And every one that hath forsaken houses, or brethren, or sisters, or father, or mother, or wife, or children, or lands, for my name's sake, shall receive an hundredfold, and shall inherit everlasting life. 30 But many that are first shall be last; and the last shall be first.
What Jesus is telling us here is that man it is impossible to live up to the standards of God, but salvation is possible through the works of God, since God is omnipotent and nothing is impossible with him. So salvation is out of our hands, with one exception:
John 3:13 through 19 And no man hath ascended up to heaven, but he that came down from heaven, even the Son of man which is in heaven. 14 And as Moses lifted up the serpent in the wilderness, even so must the Son of man be lifted up: 15 That whosoever believeth in him should not perish, but have eternal life. 18 He that believeth on him is not 16 For God so loved the world, that he gave his only begotten Son, that whosoever believeth in him should not perish, but have everlasting life. 17 For God sent not his Son into the world to condemn the world; but that the world through him might be saved. condemned: but he that believeth not is condemned already, because he hath not believed in the name of the only begotten Son of God. 19 And this is the condemnation, that light is come into the world, and men loved darkness rather than light, because their deeds were evil.
This is the most quoted Scripture when talking about salvation:
John 3:16 and 17 For God so loved the world, that he gave his only begotten Son, that whosoever believeth in him should not perish, but have everlasting life. 17 For God sent not his Son into the world to condemn the world; but that the world through him might be saved.
Even though this is sufficient to explain God's gift of Salvation, lets consider the entire passage of Matthew 19:23 through 30 and see if we can extract more from it, and how that is related to Johns 3:13 through 19.
In verse 23 Jesus says that a rich man shall hardly enter into the kingdom of heaven.
This does not say as some believe that a rich man cannot enter heaven, only that he shall hardly enter. What Jesus is actually saying is that a rich man trusting in his riches gives little consideration to his eternity. We see this today in the U.S. where we as a nation are wealthy by comparison to most of the World.
In verse 24 Jesus says it is easier for a camel to go through the eye of a needle than for a rich man to enter Heaven, an impossible task in our material world, but not in God's spiritual world where physics has no dominion. This brings to my mind many instances in the movies where an object becomes fluid and goes through a small opening. Spirits have no material form and it is as easy for a camel in the Spirit realm to go through the eye of a needle as for our sun to come up in the morning.
In verses 25 and 26 Jesus is actually telling his Apostles that they have to quit thinking in Worldly terms and start thinking in Heavenly terms.
At this point we need to look at another of Jesus teachings:
Matthew 5:2 through 12 And he opened his mouth, and taught them, saying, 3 Blessed are the poor in spirit: for theirs is the kingdom of heaven. 4 Blessed are they that mourn: for they shall be comforted. 5 Blessed are the meek: for they shall inherit the earth.
Mat 5:6 Blessed are they which do hunger and thirst after righteousness: for they shall be filled. 7 Blessed are the merciful: for they shall obtain mercy. 8 Blessed are the pure in heart: for they shall see God. 9 Blessed are the peacemakers: for they shall be called the children of God. 10 Blessed are they which are persecuted for righteousness' sake: for theirs is the kingdom of heaven. 11 Blessed are ye, when men shall revile you, and persecute you, and shall say all manner of evil against you falsely, for my sake. 12 Rejoice, and be exceeding glad: for great is your reward in heaven: for so persecuted they the prophets which were before you.
When Peter asked Jesus "27 Then answered Peter and said unto him, Behold, we have forsaken all, and followed thee; what shall we have therefore?" the remainder of this passage is contingent on Matthew 5:2 through 12, since these are the basic concepts of being a Christian, and are the very same characteristics Jesus himself demonstrated on the Earth.
Now that we have established that punishment is eternal for the unsaved, can we find any reason for being eternal?
The Lake of fire was actually created as a place of eternal punishment for Satan and his demons, and that was in response to their rebellion. Now it appears that since man has also rebelled against God that a just God has determined that man should have equal justice with them.
John 5:26 through 30 For as the Father hath life in himself; so hath he given to the Son to have life in himself; 27 And hath given him authority to execute judgment also, because he is the Son of man. 28 Marvel not at this: for the hour is coming, in the which all that are in the graves shall hear his voice, 29 And shall come forth; they that have done good, unto the resurrection of life; and they that have done evil, unto the resurrection of damnation. 30 I can of mine own self do nothing: as I hear, I judge: and my judgment is just; because I seek not mine own will, but the will of the Father which hath sent me.
How those Scriptures interact with John 3:16 and 17 is that Jesus who came down to earth and lived in a human body is well aware of our strengths and weaknesses. He knows that we do not have the strength to live the life God intended for us, but he also knows that we have the innate ability to trust in his sacrifice to atone for our sins. He also knows that we will sometimes be given the spirit of unbelief in our salvation by Satan in an attempt to steal our souls away from God. However he gave us a way to counter Satan, in that:
1st John 1:9 If we confess our sins, he is faithful and just to forgive us our sins, and to cleanse us from all unrighteousness.
If we believe that Jesus death on the cross paid our sin debt in full and if we confess our sins and ask God for his forgiveness he will forgive and we have been saved, and will inherit eternal life, and we must adhere to this belief since it is the only basis for Salvation and Satan has no power to change that.