6 But as some of these men impudently assert that the apostles, when preaching among the Jews, could not declare to them another god besides Him in whom they (their hearers) believed, we say to them, that if the apostles used to speak to people in accordance with the opinion instilled into them of old, no one learned the truth from them, nor, at a much earlier date, from the Lord; for they say that He did Himself speak after the same fashion. Wherefore neither do these men themselves know the truth; but since such was their opinion regarding God, they had just received doctrine as they were able to hear it.
According to this manner of speaking, therefore, the rule of truth can be with nobody; but all learners will ascribe this practice to all [teachers], that just as every person thought, and as far as his capability extended, so was also the language addressed to him. But the advent of the Lord will appear superfluous and useless, if He did indeed come intending to tolerate and to preserve each man's idea regarding God rooted in him from of old. Besides this, also, it was a much heavier task, that He whom the Jews had seen as a man, and had fastened to the cross, should be preached as Christ the Son of God, their eternal King.
Since this, however, was so, they certainly did not speak to them in accordance with their old belief. For they, who told them to their face that they were the slayers of the Lord, would themselves also much more boldly preach that Father who is above the Demiurge, and not what each individual bid himself believe [respecting God]; and the sin was much less, if indeed they had not fastened to the cross the superior Saviour (to whom it behooved them to ascend), since He was impassible.
For, as they did not speak to the Gentiles in compliance with their notions, but told them with boldness that their gods were no gods, but the idols of demons; so would they in like manner have preached to the Jews, if they had known another greater or more perfect Father, not nourishing nor strengthening the untrue opinion of these men regarding God. Moreover, while destroying the error of the Gentiles, and bearing them away from their gods, they did not certainly induce another error upon them; but, removing those which were no gods, they pointed out Him who alone was God and the true Father.
Source: Adversus haereses (New Advent)