Romans 3:3

‘For what if some were without faith? Will their want of faith make of none effect (render inoperative) the faithfulness of God?'

Taking this as the question of the supposed antagonist, the questioner is now arguing that the unfaithfulness of some among the Jews did not render inoperative God's faithfulness (the use of only ‘some' being without faith does of course go against what Paul has previously said. His point has been that all were faithless). Surely, they were saying, God would still be true to His word and promises even if many among the Jews failed. And in Jewish eyes this meant that He would continue to favour Jews at the judgment. So he asks, ‘Will their want of faith make of none effect (render inoperative) the faithfulness of God?' Surely, he is saying, God will remain faithful to His covenant whatever some Jews might do. And they were right. But where their premise failed was in that they overlooked the fact that they had ALL failed.

If, however we take them as Paul's words, then he is arguing that the faithlessness of many Jews who did not respond to God's revelation (and who had rejected their Messiah), did not demonstrate that God had been unfaithful or prevent His faithfulness from operating (something he will prove in Chapter s 9-11 where he points out that God always has His chosen remnant to whom He is faithful). Indeed His judgment of those unbelieving Jews would rather demonstrate His faithfulness, for that was what He had promised in the covenant, blessing and cursing (Leviticus 26; Deuteronomy 28). So the implication is that this argument basically underlined their own unrighteousness and unbelief, rather than challenging His faithfulness, for His faithfulness was still operative in salvation towards those who did believe, while it was also being operative in respect of those who would be judged. The former would be blessed and the latter cursed in accord with Deuteronomy 28.