That's exactly what I'm trying to point out: if the god of the Bible can change the notion of justice (opening exceptions from the natural law which himself supposedly created) whenever he wants then he cannot be a god, because one of the characteristics of the God is being perfect and immutable, if he can "change his mind" about what is justice then he's mutable and mutability is not perfect  

 Did you read the except from the Summa?  It addresses that very question.