stuartcr: "I believe just is something for us humans here on earth, besides, how do you know God is perfectly just?"
The Bible tells me that God is just. Christ has said that God is just and the prophets and apostles have attested that God is perfectly just.
These are all trustworthy sources that have been tested for many centuries. Besides, logic tells us that if God is the creator of all things, He is by definition just. It would be like questioning the designer of a board game whether the rules he wrote are right. The designer establishes the rules and conduct of the game.
If you believe that God is the creator of all things, you must logically conclude he is just.
It does seem to all go back to the bible. If one believes in the bible as you do, then I'm sure. But not all believe in the bible as you do...and there is just no way of proving any of this. It would take a belief that I do not have in me, to believe in the bible as you do. I cannot force myself to believe.
How does being the creator, make God by definition just? As I stated earlier, I believe God is above what we consider justice.