The previous verse Al-Baqarah 2:100 ⧉ had told us how the breaking of pledges and disobedience had become a regular habit with the Jews. The present verse Al-Baqarah 2:101 ⧉ gives us the latest instance, which is the most relevant to the context.
The Torah had already given the Jews the good tidings of the coming of the Holy Prophet . When he actually came with all signs which the Torah had indicated, thus confirming the Sacred Book of the Jews, a large number of them refused to accept him as a prophet. In doing this, they were, in fact, denying the Torah itself, and behaving as if they know nothing of the prophecy, or even the Torah being a Book of Allah. Thus, they were being guilty of infidelity (Kufr) even in terms of the Torah itself.