“But the Lord sits enthroned forever; he has established his throne for justice, and he judges the world with righteousness; he judges the peoples with uprightness.” (Psalm 9:7–8, ESV)
While nations of men come and go, the Lord is already enthroned and will continue on his throne for eternity. He is the true King of Kings.
And unlike the thrones of feeble sinful mankind, God’s throne is established with righteousness for the execution of justice. This means that while he may give justice, or non-justice (mercy and grace) to his subjects, we can be confident he will never issue injustice from his judgment seat.
Even the unbelievers will be dealt with in uprightness by God. How much more can we expect his uprightness in the judgment of his own?