Your body turns back into dust

For what happens to the children of man and what happens to the beasts is the same; as one dies, so dies the other. They all have the same breath, and man has no advantage over the beasts, for all is vanity. All go to one place. All are from the dust, and to dust all return. -- Ecclesiastes 3:19-20 (ESV)

Despite that the human body is considered to be "dust", a psalmist testify:

Precious in the sight of the LORD is the death of His saints. -- Psalm 116:15 (NKJV)

Your spirit returns to God

Some religions would go to the extreme to protect and preserve dead bodies (like building pyramids). However, Solomon wrote:

The dust returns to the earth as it was, and the spirit returns to God Who gave it. -- Ecclesiastes 12:7 (ESV)

This is what happened to Jesus when he died on the cross:

Then Jesus, calling out with a loud voice, said, “Father, into your hands I commit my spirit!”

And having said this he breathed his last.

-- Luke 23:46 (ESV)

Paul also compares our "outer self" (human body) with temporary earthly tents housing our "inner self" (spirit), with an eternal heavenly building (exalted body) which God would provide.

Though our outer self is wasting away, our inner self is being renewed day by day.

For this light momentary affliction is preparing for us an eternal weight of glory beyond all comparison, as we look not to the things that are seen but to the things that are unseen. For the things that are seen are transient, but the things that are unseen are eternal. For we know that if the tent that is our earthly home is destroyed, we have a building from God, a house not made with hands, eternal in the heavens. For in this tent we groan, longing to put on our heavenly dwelling, if indeed by putting it on we may not be found naked. For while we are still in this tent, we groan, being burdened — not that we would be unclothed, but that we would be further clothed, so that what is mortal may be swallowed up by life.

He Who has prepared us for this very thing is God, Who has given us the Spirit as a guarantee. So we are always of good courage.

We know that while we are at home in the body we are away from the Lord, for we walk by faith, not by sight. Yes, we are of good courage, and we would rather be away from the body and at home with the Lord. So whether we are at home or away, we make it our aim to please Him.

-- 2 Corinthians 4:16 - 5:9 (ESV)

This means the purpose of life is to "make it our aim to please Him". This is the answer to the question of which Atheists finds very difficult to answer.

Peter also confirms this reasoning:

Therefore, brethren, be even more diligent to make your call and election sure, for if you do these things you will never stumble; for so an entrance will be supplied to you abundantly into the everlasting kingdom of our Lord and Savior Jesus Christ.

For this reason I will not be negligent to remind you always of these things, though you know and are established in the present truth. Yes, I think it is right, as long as I am in this tent, to stir you up by reminding you, knowing that shortly I must put off my tent, just as our Lord Jesus Christ showed me. Moreover I will be careful to ensure that you always have a reminder of these things after my decease.

-- 2 Peter 1:10-15 (NKJV)

You will temporarily be unconscious

Some denominations belief that you would go immediately to "paradise" in a conscious state based on Jesus' words to the criminal who was dying with at the crucifixion:

And he (the criminal) said, “Jesus, remember me when you come into your kingdom.”
And he (Jesus) said to him, “Truly, I say to you, today you will be with me in Paradise.”

-- Luke 23:42-43 (ESV)

The problem is that the original Greek manuscript did not contain commas (,) like the English translation. This translation means that Jesus would see him the same day in Paradise, which contradict Peter (1 Peter 3:18-20) and possibly Paul too (Ephesians 4:9-10). Other translations read:

And he said to him, "Truly I say to you today, you will be with me in the Paradise." -- Luke 23:43 (REV)

This means, that Jesus is telling him today about some event that will happen some time in the future.

Contrary to many denominations that belief in a second chance in purgatory, Job said:

But a man dies and is laid low; man breathes his last, and where is he?

As waters fail from a lake and a river wastes away and dries up, so a man lies down and rises not again;

till the heavens are no more he will not awake or be roused out of his sleep.

Oh that you would hide me in Sheol, that you would conceal me until your wrath be past, that you would appoint me a set time, and remember me!

If a man dies, shall he live again?

All the days of my service I would wait, till my renewal should come. You would call, and I would answer you; you would long for the work of your hands.

-- Job 14:10-15 (ESV)

This implies Job beliefs that at death we would "sleep" and that our spirits would be "concealed" in "Sheol" (not hell nor purgatory) until "a set time" when they would be "renewed" and would be able to "answer" again.

David also believed that one "sleeps" at death:

Consider and answer me, O LORD my God; light up my eyes, lest I sleep the sleep of death -- Psalm 13:3 (ESV)

Daniel also confirms:

And many of those who sleep in the dust of the earth shall awake... -- Daniel 12:2 (ESV)

Even Jesus said that death is like "sleeping":

While he was saying these things to them, behold, a ruler came in and knelt before him, saying, “My daughter has just died, but come and lay your hand on her, and she will live.”

And Jesus rose and followed him, with his disciples.

...

And when Jesus came to the ruler’s house and saw the flute players and the crowd making a commotion, he said, “Go away, for the girl is not dead but sleeping.”

And they laughed at him. But when the crowd had been put outside, he went in and took her by the hand, and the girl arose. And the report of this went through all that district.

-- Matthew 9:18-19,23-26 (ESV)

Paul even refers to dead people as those "who are asleep":

Then he appeared to more than five hundred brothers at one time, most of whom are still alive, though some have fallen asleep. -- 1 Corinthians 15:6 (ESV)

and

But we do not want you to be uninformed, brothers, about those who are asleep, that you may not grieve as others do who have no hope. For since we believe that Jesus died and rose again, even so, through Jesus, God will bring with him those who have fallen asleep. For this we declare to you by a word from the Lord, that we who are alive, who are left until the coming of the Lord, will not precede *those who have fallen asleep. For the Lord himself will descend from heaven with a cry of command, with the voice of an archangel, and with the sound of the trumpet of God. And the dead in Christ will rise first. Then we who are alive, who are left, will be caught up together with them in the clouds to meet the Lord in the air, and so we will always be with the Lord. Therefore encourage one another with these words. -- 1 Thessalonians 4:13-18

You will be resurrected with a new spiritual body

And many of those who sleep in the dust of the earth shall awake, some to everlasting life, and some to shame and everlasting contempt. And those who are wise shall shine like the brightness of the sky above; and those who turn many to righteousness, like the stars forever and ever. -- Daniel 12:2-3 (ESV)

Which possibly implies the righteous will receive an extraordinary shining body (but of course this could also be interpreted symbolically).

But someone will ask, “How are the dead raised? With what kind of body do they come?” You foolish person! What you sow does not come to life unless it dies. And what you sow is not the body that is to be, but a bare kernel, perhaps of wheat or of some other grain.

But God gives it a body as He has chosen, and to each kind of seed its own body. For not all flesh is the same, but there is one kind for humans, another for animals, another for birds, and another for fish. There are heavenly bodies and earthly bodies, but the glory of the heavenly is of one kind, and the glory of the earthly is of another. There is one glory of the sun, and another glory of the moon, and another glory of the stars; for star differs from star in glory.

So is it with the resurrection of the dead. What is sown is perishable; what is raised is imperishable. It is sown in dishonor; it is raised in glory. It is sown in weakness; it is raised in power. It is sown a natural body; it is raised a spiritual body. If there is a natural body, there is also a spiritual body.

-- 1 Corinthians 15:35-44 (ESV)

You will be judged

Contrary to the view that God will save everyone regardless, we read in the Bible:

We will all stand before the judgment seat of God;

for it is written,

“As I live, says the Lord, every knee shall bow to me, and every tongue shall confess to God.”

So then each of us will give an account of himself to God.

-- Romans 14:10-12 (ESV)

Ultimately the LORD (YHVH) God is the final "Judge of all the earth" ((Genesis 18:25; Psalm 7:8-11; 9:7-8,19; 50:4-6; 67:4; 75:2; 96:10-13; 98:9; Isaiah 3:13-14;33:22; 51:5; Jeremiah 11:20; Ezekiel 7:3,8,27). However,

Jesus cried out and said,

“Whoever believes in me, believes not in me but in him who sent me. And whoever sees me sees him who sent me. I have come into the world as light, so that whoever believes in me may not remain in darkness. If anyone hears my words and does not keep them, I do not judge him; for I did not come to judge the world but to save the world.

The one who rejects me and does not receive my words has a judge; the word that I have spoken will judge him on the last day.

For I have not spoken on my own authority, but the Father Who sent me has Himself given me a commandment — what to say and what to speak. And I know that His commandment is eternal life. What I say, therefore, I say as the Father has told me.”

-- John 12:44-50 (ESV)

Therefore, Christ will "acknowledge" or "deny" people before his God the Father. Those who are denied, will be judged by the Father Who has the final say because "His commandment is eternal life".

“Do not fear those who kill the body but cannot kill the soul.

Rather fear him who can destroy both soul and body in hell.

Are not two sparrows sold for a penny? And not one of them will fall to the ground apart from your Father. But even the hairs of your head are all numbered. Fear not, therefore; you are of more value than many sparrows.

• So everyone who acknowledges me before men, I also will acknowledge before my Father who is in heaven,
• but whoever denies me before men, I also will deny before my Father who is in heaven.

-- Matthew 10:28-33 (ESV)

And a few chapters later in even more detail when Jesus said:

“When the Son of Man comes in his glory, and all the angels with him, then he will sit on his glorious throne.

Before him will be gathered all the nations, and he will separate people one from another as a shepherd separates the sheep from the goats. And he will place the sheep on his right, but the goats on the left.

Then the King will say to those on his right, ‘Come, you who are blessed by my Father, inherit the kingdom prepared for you from the foundation of the world. For I was hungry and you gave me food, I was thirsty and you gave me drink, I was a stranger and you welcomed me, I was naked and you clothed me, I was sick and you visited me, I was in prison and you came to me.’

Then the righteous will answer him, saying, ‘Lord, when did we see you hungry and feed you, or thirsty and give you drink? And when did we see you a stranger and welcome you, or naked and clothe you? And when did we see you sick or in prison and visit you?’

And the King will answer them, Truly, I say to you, as you did it to one of the least of these my brothers, you did it to me.’

“Then he will say to those on his left, Depart from me, you cursed, into the eternal fire prepared for the devil and his angels. For I was hungry and you gave me no food, I was thirsty and you gave me no drink, I was a stranger and you did not welcome me, naked and you did not clothe me, sick and in prison and you did not visit me.’

Then they also will answer, saying, ‘Lord, when did we see you hungry or thirsty or a stranger or naked or sick or in prison, and did not minister to you?’

Then he will answer them, saying, ‘Truly, I say to you, as you did not do it to one of the least of these, you did not do it to me.’

And these will go away into eternal punishment, but the righteous into eternal life.”

-- Matthew 25:31-46 (ESV)

Therefore, it makes sense that Paul wrote:

For we must all appear before the judgment seat of Christ, so that each one may receive what is due for what he has done in the body, whether good or evil. -- 2 Corinthians 5:10 (ESV)

The author of the book of Hebrews also confirms:

And just as it is appointed for man to die once, and after that comes judgment, so Christ, having been offered once to bear the sins of many, will appear a second time, not to deal with sin but to save those who are eagerly waiting for him. -- Hebrews 9:27-28 (ESV)

John saw this vision:

And I saw the dead, small and great, standing before God, and books were opened. And another book was opened, which is the Book of Life. And the dead were judged according to their works, by the things which were written in the books. The sea gave up the dead who were in it, and Death and Hades delivered up the dead who were in them. And they were judged, each one according to his works. Then Death and Hades were cast into the lake of fire. This is the second death. And anyone not found written in the Book of Life was cast into the lake of fire. -- Revelation 20:12-15 (NKJV)

The fate of those who are acknowledged by Christ

These people will live with Jesus in His Father's house:

In my Father’s house are many rooms. If it were not so, would I have told you that I go to prepare a place for you? And if I go and prepare a place for you, I will come again and will take you to myself, that where I am you may be also. And you know the way to where I am going.” -- John 14:2-4 (ESV)

Jesus also quotes in Mark 9:48:

“For as the new heavens and the new earth that I make shall remain before me, says the LORD, so shall your offspring and your name remain. From new moon to new moon, and from Sabbath to Sabbath, all flesh shall come to worship before Me", declares the LORD.
“And they shall go out and look on the dead bodies of the men who have rebelled against me. For their worm shall not die, their fire shall not be quenched, and they shall be an abhorrence to all flesh.”

-- Isaiah 66:22-24 (ESV)

John saw these visions:

Now I saw a new heaven and a new earth, for the first heaven and the first earth had passed away. Also there was no more sea. Then I, John, saw the holy city, New Jerusalem, coming down out of heaven from God, prepared as a bride adorned for her husband.

And I heard a loud voice from heaven saying, “Behold, the tabernacle of God is with men, and He will dwell with them, and they shall be His people. God Himself will be with them and be their God. And God will wipe away every tear from their eyes; there shall be no more death, nor sorrow, nor crying. There shall be no more pain, for the former things have passed away.”

Then He who sat on the throne said, “Behold, I make all things new.”
And He said to me, “Write, for these words are true and faithful.”
And He said to me, “It is done! I am the Alpha and the Omega, the Beginning and the End. I will give of the fountain of the water of life freely to him who thirsts. He who overcomes shall inherit all things, and I will be his God and he shall be My son.”

-- Revelation 21:1-7 (NKJV)

and

And he showed me a pure river of water of life, clear as crystal, proceeding from the throne of God and of the Lamb. In the middle of its street, and on either side of the river, was the tree of life, which bore twelve fruits, each tree yielding its fruit every month. The leaves of the tree were for the healing of the nations. And there shall be no more curse, but the throne of God and of the Lamb shall be in it, and His servants shall serve Him. They shall see His face, and His name shall be on their foreheads. There shall be no night there: They need no lamp nor light of the sun, for the Lord God gives them light. And they shall reign forever and ever. -- Revelation 22:1-5 (NKJV)

The fate of those who are denied by Christ

Contrary to the view that those who are condemned will seize to exist, Jesus said:

These will go away into eternal punishment -- Matthew 25:46 (ESV)

Jesus also warned:

If your hand causes you to sin, cut it off. It is better for you to enter life crippled than with two hands to go to hell, to the unquenchable fire. And if your foot causes you to sin, cut it off. It is better for you to enter life lame than with two feet to be thrown into hell. And if your eye causes you to sin, tear it out. It is better for you to enter the kingdom of God with one eye than with two eyes to be thrown into hell, "where their worm does not die and the fire is not quenched". -- Mark 9:43-48 (ESV)

Jude also wrote:

Just as Sodom and Gomorrah and the surrounding cities, which likewise indulged in sexual immorality and pursued unnatural desire (Genesis 19:1-29), serve as an example by undergoing a punishment of eternal fire. -- Jude 1:7 (ESV)

John saw this vision:

The cowardly, unbelieving, abominable, murderers, sexually immoral, sorcerers, idolaters, and all liars shall have their part in the lake which burns with fire and brimstone, which is the second death. -- Revelation 21:8

This is why we need to be saved.