Hello shalet,
Sin is not an illusion, it is very real..and it has the begging and that implies it will have an end
To be exact, sin means "separation from God" when you sin..that action of sinning separates you from God Almighty, though the case is not terminal as you still have the chance of a reunion through repentance.
You dont have to have a judgement book..coz Jah said do this and this and that you should not do..so if you go contrary to what God said then you sin and consequently you shall be judged.
If you say to do good is humanity then you agree with me that the nature of man is to do good..now pause and ponder for a minute...why is it in human nature to do good...why should it not be the other way around? that to do evil is humanity and thus doing good should be something out of normal?
It is simply because when Jah created man, He created him and put in him this trait of goodness..its only thru the act of diisobedience that man turned to doing bad.
about being rewarded, I can be in line with you if you say "do good, not in expectancy of a reward, but because you have to" thats right..but then it is undeniable that Jah Almighty will reward the good-doers and punish the evil one...for it is written that "The wages of sin is death but the gift of Jah is eternal life" therefore Jah do reward those who do good.