Romans 3:5

‘But if our unrighteousness commend the righteousness of God, what shall we say? Is God unrighteous who visits with wrath? (I speak after the manner of men.)

OK, says the theoretical questioner, if that is so it means that our unrighteousness is commending the righteousness of God. And that being so surely it is unrighteous of God to visit us with wrath. The idea that this suggestion could be made so appals Paul that he immediately assures his readers that he is speaking ‘after the manner of men'. He does not want them to think that he has any doubts on the matter.

We can see here the subtlety of Jewish thinking. They considered that by their unrighteousness Jews were actually highlighting the righteousness of God, as He forgave them their sins and received them into eternal life regardless of their behaviour (something already refuted in chapter 2). Thus why should God be wrath with them? One thing that they overlooked here was that God's wrath was not just His reaction to them as such. It was His reaction to sin because of His very nature. He was of such a nature that He would not overlook sin in anyone.