If I'm somehow w/o 'sin', but do not believe in the existence of a resurrected Jesus, it is not possible to enter heaven.
If I commit 'sin', but believe in a resurrected Jesus, it is still possible to enter heaven.
1. Hence, do the concepts of 'sin' even matter at all?
2. Also, is earnest lack in belief itself considered an 'immoral' action to God? Isn't unbelief instead an amoral action/event/cognitive construct/other --- regardless of what we subjectively define as moral/immoral (or) sin/no sin?
And last, seems as though, at least from the Christian perspective anyways, that the lack in belief of Jesus deems an eternal separation from God... To instead dwell in a possible eternal place of 'discomfort'. What if the 'soul' wishes to repent, in a manor which might please God after human death? The human's fate seems sealed at human death ---> 'forever'.
3. Is this how God's 'justice' works?
You need shorter answers possibly? Keeping in mind the 1rst 2 propositions of the OP post are refuted by 1rst John as shown in post #2 and just above in post 12, here are short answers you can see from 1rst John:
"1. Hence, do the concepts of 'sin' even matter at all?"
-- Yes, profoundly so, as you see in 1rst John chapter 1-2 as above, for instance (and in many other places in the New Testament). After being a believer, to be cleansed of any subsequent serious sins one
must confess them. Without that cleansing, one will become alienated from God, and unless one eventually turns like the prodigal of Luke chapter 15, unless that turn and confession happens, the outcome would be the "second death" in the Lake of Fire. So, sin is of very great significance.
"2. Also, is earnest lack in belief itself considered an 'immoral' action to God? Isn't unbelief instead an amoral action/event/cognitive construct/other --- regardless of what we subjectively define as moral/immoral (or) sin/no sin?"
That depends on just what you're disbelieving in precisely.... If merely for instance some random theology viewpoint one might hear a lot in some church (and some other such in other churches), that's of little import to disbelieve in pretty often. One cannot disbelieve in Christ without ever really getting to real gospel message (regardless of if one
thinks one heard it).
It would mean something to really get it (many never have) just what Christ said, and has done for us, and then to reject that -- a far more significant thing, which actually isn't so common I think. Most just never really got the real message, cause it's not even known in some churches, or poorly communicated in many also.
"3. Is this how God's 'justice' works?"
That's directly answered in Romans chapter 2, verses 6-16. Which begins:
Romans 2:6 God "will repay each one according to his deeds."
See how serious that is even with just the first verse?
