The design or final cause which God had in view in the whole matter of the atonement is next subjoined: that He might be just, and the justifier (Rom. 3:26). The allusion is to the concurrence or harmony of these two perfections of God. The word JUST, applied to God, means that He asserts just claims and inflicts just punishment. It is a perversion of language to interpret the term as if it could mean anything else than justice in the ordinary acceptation of the word among men made in the image of God. The contrast in which it is placed to divine forbearance, and the allusion to the propitiatory, allow no doubt as to its import Justice seemed to slumber during that period of forbearance; now it is displayed.
But this determines the character of the atonement Such language would be unmeaning, if it were not admitted that the atonement is in the proper sense of the word a satisfaction of divine justice. This single clause, therefore, fully warrants the expression in common use, notwithstanding all the objections which have been adduced against it as unfitting or unwarrantable. And when the apostle adds, “that He might be just, AND THE JUSTIFIER,” he alludes to the fact that these two apparently conflicting perfections, justice and grace, meet in full harmony on the cross: justice suffers no violence, and grace has full outlet.
The Doctrine of the Atonement, as Taught by the Apostles (Edinburgh: T&T Clark, 1870), 142-143.
(HT: The Old Guys)