Surah 2. Al-Baqara, Ayah 101

The divine writ referred to here is the Torah. By disregarding the prophecies relating to the coming of the Arabian Prophet, contained in Deuteronomy xviii, 15, 18 (see note [33] above), the Jews rejected, as it were, the whole of the revelation granted to Moses (Zamakhshari; also 'Abduh in Manar I, 397).

I think that by "the Book of God" here is meant, not the Qur-an, but the Book which the People of the Book had been given, viz., the previous Revelations. The argument is that Muhammad's Message was similar to Revelations which they had already received, and if they had looked into their own Books honestly and sincerely, they would have found proofs in them to show that the new Message was true and from God. But they ignored their own Books or twisted or distorted them according to their own fancies. Worse, they followed something which was actually false and mischeivous and inspired by the evil one. Such was the belief in magic and sorcery. These are described in the next verse in terms referring to the beliefs and practices of the "People of the Book."