Hi Glenn, great question!

You asked:
“so if Jesus' death forgave everybody for past and future sins, why do christians still threaten that you can go to hell for sinning?”

Forgiveness is an offer.

Jesus did all the work to make it possible. Jesus extends that offer to everyone.

But if you refuse it, you don’t receive it.

Imagine a wealthy man offering to pay back your debt to the bank. He has the money. He’s willing. He’s handing out the cash to you so you can go pay the bank back.

What happens if you refuse the cash?

You don’t get the money, and your debt remains unpaid.

People go to hell because they refuse the forgiveness Jesus is offering.

Jesus wants you saved. That’s why He died for your sin, to remove it, to make full forgiveness and atonement possible.

But if someone refuses His forgiveness, then they retain their sin and their debt.

If you want to see hell in action, read Isaiah 6.

God takes Isaiah into eternity. God brings Isaiah into Heaven, into the Throne Room of God, into the presence of angels.

Yet it’s hell for Isaiah. All he feels is agony and pain.

Why? Because he’s still full of his sin. In eternity, sin is agony. Our own sins torture us.

Isaiah feels the agony and torture of his own sin until God forgives him, atoning for his sin and taking it away through a sacrifice on the altar. Once Isaiah is forgiven, Heaven suddenly feels Heavenly.

Those who refuse God’s forgiveness enter eternity still possessing their sins, and their own sins torment them. This is what the Bible refers to as storing up wrath against yourself.

God doesn’t want that to happen. Jesus makes forgiveness available to absolutely everyone. He is desperate for you to accept His forgiveness and enter eternity clean, forgiven, able to enjoy it as heavenly.

But if you refuse it, you don’t get it.