Were the Talmudic Sages experts in the written Torah?
The Gemara relates that Rabbi Abbahu spoke highly of Rav Safra before a group of minim – sectarians – who arranged to free him from paying taxes for 13 years. One day they met Rav Safra and asked him to offer an interpretation of the passage in Sefer Amos (3:2) where it is taught that God favors the Jewish people, which is why he punishes them for their sins. Why would God take out His anger specifically against those whom he loves and favors?
Rav Safra did not answer their question, and they threw a scarf around his neck (either they were trying to choke him since he would not reveal the meaning, or else they took off his turban and threw it around his neck, embarrassing him). Rabbi Abbahu came upon this scene and demanded an explanation. The minim said to him that they found that the man who Rabbi Abbahu presented as a great person could not explain a passage in the Bible! Rabbi Abbahu replied that Rav Safra was great in his knowledge of the oral law, but not of the written Torah. He further explained that the Babylonian Sages spent all of their efforts studying the oral law, but since there were heretics in Israel who challenged the Sages with their interpretations of the Bible, the Sages in Israel needed to study the written Torah in order to respond to them. In closing Rabbi Abbahu offered an explanation to the passage, that God takes out his anger slowly against the Jews, while against others he brings down a severe punishment all at once.
During Rabbi Abbahu’s time – at the end of the 3rd century CE – groups of sectarians, especially Christians, began to come to positions of power in Israel, which is how they had the ability to influence tax collection on individuals. These sectarians were very interested in the Bible and its interpretation, which is why they felt deceived when they discovered that Rav Safra was not as great an expert in the field as they had supposed.