HMMMmmm...
John 3:18 kjv
He that believeth on him is not condemned: but he that believeth not is condemned already, because he hath not believed in the name of the only begotten Son of God.
What boogers up this entire discussion is it’s generally not observed that both sin and forgiveness have two sides.
Sin has BOTH an UNCONDITIONAL PENALTY (Death, Rom. 6:23), which is uniform for all sin, and CONDITIONAL CONSEQUENCES that vary basis the sin. Likewise forgiveness is two-sided: I can forgive you for sin against me, and — conditioned upon your repentance — God can change the relational consequences tied to that sin. But neither of us could have ever changed the Unconditional Penalty for that sin; somebody had to be executed for it.
It was that Penalty that was unconditionally forgiven at The Cross, but Conditional Consequences of varying severity remain. One Consequence of unbelief is this condemnation John writes about, here. It’s not that the blood of Jesus is insufficient to forgive unbelievers, it’s that his blood paid the Penalty — took away the Death sentence — of sin; not the Consequences. These remain, and may be mitigated (or not) basis belief, or unbelief, and our resulting relationship to God, and to one another. If the unbelieving come to believe, the Consequences of unbelief are relieved, also.
Think of this state of condemnation like people standing in the middle of a railroad track. They’re dead meat. It’s guaranteed. The train is coming, it’s NOT stopping for them; they are as good as dead as a CONDITIONAL CONSEQUENCE of their continued unbelief. And you and I know people like this; just OBSTINATE in intentional unbelief. They not only DON’T believe, they emphatically WON’T believe; they are as good as dead already. THAT is the nature of this condemnation.
But they don’t HAVE TO die; they have a choice, because Jesus paid the UNCONDITIONAL PENALTY of their unbelief at The Cross, so they aren’t chained to the rails. They may repent, and believe, and God will — under those new CONDITIONS — change their CONSEQUENCES; removing them entirely, in this case.
If they come to believe, they step off the tracks, and find life. The train is STILL coming, and it’s STILL NOT stopping, but their dire Consequences are removed as a Condition of their repentance, and belief.