ולוקשה רחמנא לנבלה!
This seems like an important point for the Talmud Bavli’s view of Torah she-ba’al peh, so I’m going giving it at least one more post.
The background is that Rabbi Akiva and the Sages disagree on whether the impurity of an idol works like that of a niddah or like that of a sherets. Each quotes a biblical verse for support. The rishonim understand the impurity of idols to be a rabbinic decree, so those verses are really asmakhtot, not sources. But then Rabbah qualifies the Sages’ opinion so that the impurity of idols is more like that of a nevelah than a sherets. The Gemara objects, “Then let the Merciful One [in the Torah] compare [the impurity of idols] to nevelah!”
Why does the Gemara expect the Torah to match a much later rabbinic decree?