What "book" is referred to in the phrase "People of the Book"?

The phrase "People of the Book" generally refers to religious communities that have received divine scriptures, specifically the Jews and Christians. In the Qur'an, these communities are often addressed with this term to highlight their relationship with previous revelations.

One relevant verse states: O People of the Scripture! Now hath Our messenger come unto you, expounding unto you much of that which ye used to hide in the Scripture, and forgiving much. now hath come unto you light from Allah and plain Scripture, 5:15. Here, the "Scripture" refers to the holy texts that the Jews and Christians possess, such as the Torah for the Jews and the Gospel for the Christians.

Additionally, the term "People of the Book" emphasizes the importance of the Qur'an as the final revelation, which is described as "light" and "plain Scripture," addressing the previous scriptures while guiding the believers toward the final message from Allah.

Ibn Kathir explains that these verses clarify the role of the Qur'an as a continuation of the guidance provided in earlier scriptures, which were partially concealed or misinterpreted over time. The Qur'an serves not only to clarify these earlier revelations but also to bring new insights and guidance for humanity.