“Because sin is a crime, and must be punished.”
Why must it be punished?
The goal of a punishment is to prevent future misbehavior.
We also sometimes use education to prevent future misbehavior.
Why does a being of infinite mercy need punishment? Why would an omniscient being of infinite mercy find that Punishment, suffering, is preferable to education?
And if this is about Hell, Hell is just a revenge fantasy. Not a punishment. Once we’re in the afterlife, we don’t go back to Earth. Whether we go to Heaven or Hell, we’re never going to have another chance to sin. Nothing is gained by sending a sinner to Hell.
“Why is shoplifting illegal? Its a free country isn't it?”
Free does mean choices are supported, but the choice to harm another is not a freedom that’s guaranteed.
We punish shoplifting in the hope that the criminal will not shoplift in the future.
THis is why not every single crime calls for a death sentence.