Penal substitution, as an idea, presupposes a penalty (poena) due to us from God the Judge for wrong done and failure to meet His claims. The locus classicus on this is Romans 1:18-3:20, but the thought is everywhere in the New Testament. The judicial context is a moral context, too; whereas human judicial systems are not always rooted in moral reality, the Bible treats the worlds of moral reality and of divine judgement as coinciding. Divine judgement means that retribution is entailed by our past upon our present and future existence, and God Himself is in charge of this process, ensuring that the objective wrongness and guiltiness of what we have been is always “there” to touch and wither what we are and shall be. In the words of Emil Brunner, “Guilt means that our past – that which can never be made good – always constitutes one element in our present situation.” When Lady Macbeth, walking and talking in her sleep, sees blood on her hand and cannot clean or sweeten it, she witnesses to the order of retribution as all writers of tragedy and, surely, all reflective men – certainly, those who believe in penal substitution – have come to know it: wrongdoing may be forgotten for a time, as David forgot his sin over Bathsheba and Uriah but, sooner or later, it comes back to mind, as David’s sin did under Nathan’s ministry and, at once, our attention is absorbed, our peace and pleasure are gone, and something tells us that we ought to suffer for what we have done. When joined with inklings of God’s displeasure, this sense of things is the start of hell. Now, it is into this context of awareness that the model of penal substitution is introduced…
From: “What Did the Cross Achieve: The Logic of Penal Substitution,” in The Collected Shorter Writings of J. I. Packer: Volume 1: Celebrating the Saving Work of God by James I. Packer (Carlisle: Paternoster Press, 1998), pp. 108-109. This article was originally published in 1974.