Perhaps the formula that Luther used that is most famous and most telling at this point is his formula simul justus et peccator. And if any formula summarizes and captures the essence of the Reformation view, it is this little formula. Simul is the word from which we get the English word simultaneously. Or, it means ‘at the same time.’ Justus is the Latin word for just or righteous. And you all know what et is. Et the past tense of the verb ‘to eat.’ Have you et your dinner? No, you know that’s not what that means. You remember in the death scene of Caesar after he’s been stabbed by Brutus he says, “Et tu, Brute?” Then fall Caesar. And you too Brutus? It simply means and. Peccator means sinner.
And so with this formula Luther was saying, in our justification we are one and the same time righteous or just, and sinners. Now if he would say that we are at the same time and in the same relationship just and sinners that would be a contradiction in terms. But that’s not what he was saying. He was saying from one perspective, in one sense, we are just. In another sense, from a different perspective, we are sinners; and how he defines that is simple. In and of ourselves, under the analysis of God’s scrutiny, we still have sin; we’re still sinners. But, by imputation and by faith in Jesus Christ, whose righteousness is now transferred to our account, then we are considered just or righteous. This is the very heart of the gospel.
Will I be judged in order to get into heaven by my righteousness or by the righteousness of Christ? If I had to trust in my righteousness to get into heaven, I would completely and utterly despair of any possibility of ever being redeemed. But when we see that the righteousness that is ours by faith is the perfect righteousness of Christ, then we see how glorious is the good news of the gospel. The good news is simply this, I can be reconciled to God, I can be justified by God not on the basis of what I did, but on the basis of what’s been accomplished for me by Christ.
But at the heart of the gospel is a double-imputation. My sin is imputed to Jesus. His righteousness is imputed to me. And in this two-fold transaction we see that God, Who does not negotiate sin, Who doesn’t compromise His own integrity with our salvation, but rather punishes sin fully and really after it has been imputed to Jesus, retains His own righteousness, and so He is both just and the justifier, as the apostle tells us here. So my sin goes to Jesus, His righteousness comes to me in the sight of God.