Righteous to forgive unrighteousness

It’s common among evangelicals to say that the gospel is about God solving the tension between His justice and His mercy. As a just God, He must punish sin; as a merciful God, He seeks to save. The cross combines the two.

At one level, I have no problem with this. But it is problematic both theologically and exegetically. Theologically because it reifies the attributes of God and implicitly denies the simplicity of God. Exegetically because, as John says, it is precisely the “righteous” God who “forgives us our sins and cleanses us from all unrighteousness.” Forgiveness is not a contradiction of God’s justice, but a manifestation of His justice.