In what way would it be "justice" to punish people everlastingly, particularly when the principles underpinning this supposed justice system are in no way obvious, as you already admitted?
The way to salvation/grace/mercy may not be obvious... but I didn't say (admit) that sin/wickedness wasn't obvious.
We violate our own moral consciences when we sin (begin to sin). We may continue in such behavior as to
burn/sear and ruin our own moral compass/conscience... but we still have been given a conscience for knowing
when we are FIRST committing moral evil.
To answer your question, however, (in what way would it be "justice" to punish people everlastingly?) we
would first have to make a distinction between "separation" and "punishment." God is Perfect and absolutely
Holy... God will not fellowship with a morally tainted creation/creature (freewill creature) unless that creature
has been made righteous (in Christ Jesus through His perfect Sacrifice). So if someone taints themselves with
committing moral evil then God will logically "separate" them from His affectionate fellowship AND from the
new heaven and new earth. This separation is due to their "taintedness." (self-taintedness and guiltiness.
God doesn't punish the innocent.)
Now the punishment is for exact actions. This is why eternal hell can be thought of as "unequal punishment
AND separation." Everyone in the afterlife receiving justice will receive "unequal" punishment BASED ON
their exact infractions.
Now there is also something eternal about the nature of sin itself. Sin stays in the historical record from this
temporary creation forever. If sin (moral evil) is never responded to with perfect justice, then it would remain
in existence (the historical record from the temporary creation) as a mockery against the JUSTICE and holiness
of God. It is the RIGHTNESS/righteousness of justice that makes punishing eternal sin/wickedness a logical
retribution.
It is the nature of sin itself to be eternal in multiple ways. There is no such thing as a finite sin. Just think
about if you kill someone... you affect their eternity forever.... by sending them into eternity sooner than
if you had NOT killed them. If you rape a woman... you will affect her life and the things she might have
done in her life. You will logically affect her eternity (either rewards or consequences)by changing/altering
her life experiences and circumstances. This is true for any sin you commit against another person that
has an effect on them. You change or contribute to affecting their eternity (their life) in some way.
Eternity involves eternal rewards for an adopted person/child of God and eternal consequences for the
disobedient slave (owned by God...but not an adopted child) who must pay for all of their sin debt.
An imperfect person can clearly never reach completely paying for their sin debt (especially IF they are
continuing to sin in the afterlife). They could eternally approach payment but never actually reach
complete payment.
We are just barely scratching the surface here on how it is the nature of "sin" (wickedness) to be
eternal and NOT finite. We are all (all humans and angels) eternal beings...which means we will
exist forever. We as humans are created in the Image of God (not physical image but rather
spiritual and conscious Image of God) and we are eternally going to exist in some form forever.
Most will "exist" in the afterlife and receive consequences... while others will have "life" in the
afterlife and receive rewards by God's incredible (unobligated) unfathomable GRACE/mercy.
So there are multiple reasons here involving both "separation" of an eternal being who is tainted
AND "punishment" for exact actions which can not be wrongfully lumped together as though there
is not distinction between separation and unequal punishment.
Good question.... even if the answer is not what any of us want to hear.
