To better understand the cross of Christ we should turn to penal substitution and natural law theory. Pairing penal substitution with natural law theory will strike some readers as very odd. But penal substitution needs natural law theory, because penal substitution depends upon the claim that God cannot let sins go unpunished.
Not everyone delights in natural law theory, of course. Evangelical musings on natural law theory, if they occur at all, probably resemble evangelical attitudes towards transubstantiation — now there’s something that’s not simply false, but obviously so. Surely natural law theory is godless, appealing to technical descriptions of the natural world instead of the Bible. Surely natural law theory is papist, the preserve of Roman Catholics trusting in St. Thomas Aquinas but not St. Paul the Apostle.
On the contrary, evangelicals should embrace natural law theory, and a negative attitude towards it betrays a misunderstanding of what evangelicals need in order to defend their account of the atoning work of Jesus. That may sound strange, given evangelical suspicions, but it’s true regardless.
What is penal substitution?
Penal substitution is the biblical doctrine that Christ was punished for our sins so we are not punished for our sins. Consider the Statement of Faith of the National Association of Evangelicals (NAE), a statement the NAE adopted as its founding in 1942. About Jesus, the NAE says,
We believe in the deity of our Lord Jesus Christ, in His virgin birth, in His sinless life, in His miracles, in His vicarious and atoning death through His shed blood, in His bodily resurrection, in His ascension to the right hand of the Father, and in His personal return in power and glory.
For our purposes, the most important phrase concerns Christ’s vicarious and atoning death. This statement proclaims both that Christ died in our place (his death was vicarious) and that Christ’s death satisfied God’s justice against sin (it was atoning).
Harold Ockenga, the first NAE president, wrote a book, Our Evangelical Faith, as an exposition of the NAE Statement of Faith. Though he writes only for himself, Ockenga nevertheless offers insight into what evangelicals in the 1940s believed about Christ’s death. Ockenga writes, “This shedding of blood was ‘atoning.’ That means that it was a death on account of and for sin. God’s justice was satisfied in the death of the Lamb of God.” He adds, “This sacrifice was vicarious, that is, a substitution for others.”
So Christ’s death was substitutionary, and Christ’s death satisfied divine justice. On the cross, Christ received the punishment I deserve for my sins. I am not punished for my sins, but he was. We remember these solemn truths not just once a year but Sunday to Sunday, and moment by moment.
What Moral Theory Supports Penal Substitution?
We should explore what kind of moral framework best supports these beliefs.
We can start by asking the opposite question: What kind of moral framework most easily supports a rival view? The answer is straightforward: If God’s will alone determines morality at each and every moment, then Christ’s death on the cross need not be taken as a satisfaction of divine wrath for my sins. If God arranges the moral furniture of the universe at his will, we should conclude that he could have achieved my forgiveness without any punishment at all. If God has no internal obligation to punish sins, he can forgive our sins freely without satisfaction. On the cross, according to one rival view, Jesus did not pay for my sins; instead, he offered us an example of perfect obedience and sacrificial love.
The biblical evidence speaks against such a thin account of the cross. Of course, the death of Jesus does offer us an example of perfect obedience and sacrificial love. But Christ on the cross offered more than a moral example to follow. He offered himself up to satisfy the divine justice set against our sins.
This concern to vindicate the justice of God is a biblical one. In Romans 3, Paul explains how God abides by God’s own requirements for justice. Paul recognizes a possible complaint against God’s righteousness — that God seems to have left some sins go unpunished (v. 25) — and answers this question by appealing to the cross of Christ (vv. 24–25). Paul’s concern about God’s justice makes sense only within a moral framework that says that God does not manufacture morality moment by moment.
If Paul thought God could decide what justice requires at any given moment, he would not have taken pains to defend God’s justice. He would have said instead that God decided that, in this one instance, something else was in keeping with his justice. Of course, Paul does not do that. On the contrary, he takes pains to show how God does not violate his own justice when he justifies sinners (v. 26). To what does Paul appeal in his explanation?
The cross. The cross must be something more than a mere demonstration of divine love, because God must punish every sin. God must punish every sin, but God does not need to punish each sin in each particular sinner. In his justice, God can accept a substitute to bear the punishment for another’s sins. The cross shows us, and the Bible teaches us, that God has, in his grace and kindness, done so.
What kind of moral theory helps explain God’s own understanding of what he can and cannot do? What kind of moral theory says that God knows what is just and unjust prior to making any decision at all?
The answer: natural law theory. But what is natural law theory? Natural law theory says that morality follows from the nature of things. That’s not very informative, but mathematics provides a helpful parallel to what natural law theorists believe about morality. If I talk about a triangle, you know that this triangular object is also, necessarily, a trilateral object — the three-angled thing is also a three-sided thing. Similarly, God knows what a triangle is, and when he wants to make one, he doesn’t accidentally make a square.
What is true in mathematics is true in morality. God has an eternal knowledge of the good, the true, and the beautiful. God knows what a man is, even when men do not exist. God knows what unicorns are even if (with apologies to the unicorn faithful) they do not exist. Furthermore, if God makes a man, he knows he has made an unmurderable thing. Just as triangularity brings trilaterality with it in the case of a triangle, so also do humans bring morality with them.
Opponents of natural law theory imagine God making the world and then, in a separate step, creating certain moral features of the world. Natural law theorists differ from others by believing that morality is a feature of the world that God has made; God makes things, and the morals come with those things. Most (perhaps all) Christian natural law theorists believe that God can add additional obligations that do not arise from nature — Jewish ceremonial law, for example — but the moral law is different and comes with the things God has made.
The defense of God’s justice in Romans 3 makes sense to a natural law theorist. God knows what justice requires. Justice requires the punishment of sins. So we need an explanation for how God can let sinners go unpunished. Paul provides an answer in Romans 3 and elsewhere: I am not punished for my sins, because Christ was punished for my sins. What seems to be an injustice — I am not punished — is actually just, because Christ was punished in my place.
Penal substitution says that God cannot relax the requirements for justice in order to let a single sin go unpunished. God must punish sins. God knows, from all eternity, what he can and cannot do. This eternal law of God is at the heart of natural law theory.
Good Friday reminds us that, in order to forgive sinners, God himself satisfied the requirements of his own justice. All sins must be punished, either by the sinners themselves, in hell forever, or by Jesus, on behalf of sinners, on his cross. “Jesus paid it all,” Christians sing, because he did.