The Bible (The Book) tells a unified story of humanity's guilt and God's grace. It's a writing across 66 "books" (or scrolls or paper etc.), for over 1500+ years by roughly 40 authors. Also it's across two different major religious groups. This is why people say it only has 1 real author - because all these moving parts and variables connect together to form one overarching story.
It reveals that every person has misused their free-will, choosing selfish desires, destructive habits, and rebellion against God. This is usually what's called "sin" (the quest to be free from God’s authority and accountability and to replace it with a God-free autonomy), which leaves humanity enslaved to their own emotions like anger, lust, worshipping idols (ourselves/objects/people), pride etc.

God, being perfectly just, must hold us accountable for these choices. If you think the world would be better with perfect justice enacted and that God should get rid of all "bad" people, then you'd have to understand that it'll be pointed towards you too. The punishment is death, a consequence of our abuse of free-will. Yet, in His mercy, God became human as Jesus and took that punishment upon Himself—tortured and crucified for crimes we committed. This gift of forgiveness is freely offered, but rejecting Jesus leaves us standing alone on judgement day, fully exposed to the justice we deserve. True freedom comes only when we "repent" (which means to 'change your mind'), acknowledge our guilt, accept His sacrifice, and live in gratitude for the undeserved mercy given to us. This is not earned by good deeds as bargaining tools for covering up our wrongdoings. That doesn't work in human courts and won't work in God's court. Jesus is the hope to break out of the slavery of sin which manifests (again) in our grudges, hatred, lust etc.

This life before death is only the first stage of existence for people who can introspect and self-criticise, basically humbling themselves, and not being lost in self-lies that benefit them temporarily for the sake of their comfortability. When you are saved, you are sealed for salvation and can never be unsaved, because it's based on evidence from various sources: philosophy, manuscript/archaeological/textual evidence, common sense, biblical prophecy etc.

Paul's Letter to the Romans 5:6-8
"You see, at just the right time, when we were still powerless, Christ died for the ungodly. Very rarely will anyone die for a righteous person, though for a good person someone might possibly dare to die. But God demonstrates his own love for us in this: While we were still sinners, Christ died for us."

Paul's Letter to the Romans 10:9
If you declare with your mouth, “Jesus is Lord,” and believe in your heart that God raised him from the dead, you will be saved.

Paul's Letter to Titus 3:3-5
"At one time we too were foolish, disobedient, deceived and enslaved by all kinds of passions and pleasures. We lived in malice and envy, being hated and hating one another. But when the kindness and love of God our Savior appeared, he saved us, not because of righteous things we had done, but because of his mercy."

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The verses below are confirmed to be apart of a collection of the Dead Sea Scrolls (DSS), roughly 100 years before Jesus walked on the earth. These are the Jewish scripture manuscripts that make up our Old Testament side of the Bible. I only chose the most obvious and essential ones, so they're just the tip of the iceberg of prophecies and patterns of Jesus before Christianity existed. These should be highly significant as evidence of prophecies that started as mysteries that got fulfilled in Jesus. "Fulfilment" means that in every layer, and in every way, Jesus completes the Old Testament patterns and prophecies of a coming Messiah where it felt lacking with the original examples. He is the greater and better Adam, Noah, Abraham, Issac, Jacob, Joseph, Moses, David, Solomon etc.
It's not simply "This will happen" and it comes to pass, it's much deeper than that - but that kind of simple prophecy is also fulfilled. Unlike other secular prophecies, these are not vague, and they're actually true. I'm using the NIV translation for these, but the originals say essentially the same thing.

View the translations of the DSS online here: https://dssenglishbible.com/
Another resource specifically for comparing the Great Isaiah Scroll (125 - 100 BC) and the Masoretic Text of Isaiah that was used for Bibles before the DSS were found (1009 AD): http://dss.collections.imj.org.il/chapters_pg
Translations of various NT Papyrus (the paper they used back then) + extra source for DSS translations: https://downloads.thewaytoyahuweh.com/#ancient_papyrus

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ISAIAH 7:14 (in Isaiah scrolls 1Q and 4Q65)
"Therefore the Lord himself will give you a sign: The virgin will conceive and give birth to a son, and will call him Immanuel."
(Immanuel, from the Hebrew language, means 'God with us')
(There is a double-fulfilment going on for this with Isaiah's time - then completed in Jesus' time. Read the chapter for the full context)

ISAIAH 9:6-7 (in Isaiah scrolls 1Q and 4Q57)
"For to us a child is born, to us a son is given, and the government will be on his shoulders.
And he will be called Wonderful Counselor, Mighty God, Everlasting Father, Prince of Peace.
Of the greatness of his government and peace there will be no end. He will reign on David’s throne and over his kingdom, establishing and upholding it with justice and righteousness from that time on and forever. The zeal of the Lord Almighty will accomplish this."

ZECHARIAH 2:10-11 (verse 10 is in scroll 4Q80 'Minor Prophets')
"Sing and rejoice, O daughter of Zion (Israel), for behold, I come and I will dwell in your midst", declares the Lord. "And many nations shall join themselves to the Lord in that day, and shall be my people. And I will dwell in your midst, and you shall know that the Lord of hosts has sent me to you."
(God is going to come dwell with his people, and he refers to himself in the 1st and 3rd person, like Father - Son - Holy Spirit)

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PSALM 22 (in Psalm scroll 4Q88)
"Dogs surround me, a pack of villains encircles me; they pierce my hands and my feet. [...] They divide my clothes among them and cast lots for my garment."
(Shown in the New Testament, Gospel of Matthew chapter 27, verse 35-46)
(Expanded on my "Artwork Showcase", 3rd image)

ISAIAH 53 (all in Scroll 1Q Isaiah)
[...] He was despised and rejected by mankind, a man of suffering, and familiar with pain. Like one from whom people hide their faces he was despised, and we held him in low esteem. Surely he took up our pain and bore our suffering, yet we considered him punished by God, stricken by him, and afflicted. [...] For he bore the sin of many, and made intercession for the transgressors.

Miscellaneous videos

On Evolution being correct, and being compatible with the Bible - (Note that people have pondered the interpretation of Genesis long before the 1800's, so this isn't trying to be a kind of historical revisionism):
https://www.youtube.com/watch?v=pwnerL8M1pE
https://www.youtube.com/watch?v=yf5ovSpS2GU

On why Annihilationism (punishment, then death) is a more biblically accurate depiction of hell than Eternal Torment (forever punishment):
https://www.youtube.com/watch?v=l__6DzzqEzI

On how fine-tuned the universe is for life, against all odds:
https://www.youtube.com/watch?v=ntdTWREYFJk

Entire playlist on how Genesis 1 - 11 are best read in light of evidence about the Ancient Near Eastern cultures:
https://www.youtube.com/playlist?list=PL1mr9ZTZb3TUeQHe-lZZF2DTxDHA_LFxi
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Rare Christian bangers

Skillet - Comatose

Skillet - Forgiven

DC Talk - Jesus Freak

Keith Green - Your Love Broke Through

Kanye West - Jesus Walks

Kanye West - Jesus Lord

The Plagues - Prince of Egypt