Safeguarding God's Simplicity

In Pierced for Our Transgressions: Rediscovering the Glory of Penal Substitution, the authors make the point that the doctrine of penal substitution preserves the harmony of God’s attributes, thus safeguarding his simplicity. 

[Penal substitution] preserves our understanding of God as a perfect being, all of whose attributes are in perfect harmony: love, goodness, justice, holiness, truthfulness and so on. It would be misleading to say something like ‘At the cross God’s mercy triumphed over his justice.’ That would imply that a conflict existed between God’s attributes, such that his mercy ‘won’ while his justice was frustrated. By contrast, penal substitution maintains God’s mercy and his justice, his love and his truthfulness. All are perfectly fulfilled at the cross. The writer of Psalm 85 expresses this beautifully, declaring that when the Lord saves his people, 

Love and faithfulness meet together;
righteousness and peace kiss each other.
(v. 10)

In more technical terms, penal substitution preserves what is often called the doctrine of God’s simplicity. … [This] refers to the truth that he is not composed of different ‘parts’ as though he could be dismantled somehow into separate components. We cannot speak of God’s love as though it were a ‘part’ of God, separate from his holiness. Rather, all of God’s attributes are in harmony with each other: his holiness is a loving holiness, a merciful holiness; his justice is a truthful justice, a holy justice, and so on. Within this framework, none of God’s attributes should be regarded as more ‘central’ or ‘essential’ than any of the others.

Most often, I think, those who argue against a penal substitutionary atonement make God’s love his central attribute. “God is love,” is the assertion; it’s love that wins, even over God’s other attributes. There’s no need for his justice to be expressed or his wrath to be satisfied. Or so they say.

The beauty of penal substitution, is that God wins because all that he is—all of his attributes—“are perfectly fulfilled at the cross.”