The previous verse had told us how the breaking of pledges and disobedience had become a regular habit with the Jews. The present verse 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.