Divine justice. This is one of God’s many attributes. It simply means that He independently and perfectly chooses and does what He wants to do and in the way He wants to do it. He has no outside “moral code” behind his actions and decisions. He takes no advice or counsel from anyone or any law or rule. He does not follow our fallen, preconceived assumptions of justice. Instead, He shows us what justice is by His nature. He is righteous, just and completely perfect and thus every thing He does is equally righteous, just and perfect. And if the justice of God comes from His character then we cannot push our assumptions of what justice should be upon His decisions and actions.
“But who are you, O man, to answer back to God? Will what is molded say to its molder, ‘Why have you made me like this?’ “
– Romans 9:20 ESV