4.47 – You who have been given the Book! Believe in what We have sent down, confirming what is with you
The Quran commands the People of the Book (Jews and Christians) to believe in the messenger’s recitations, claiming correspondence, with a threat attached. On the Quran’s approach to the People of the Book, see the comments at 98.1.
The Quran frequently states that its contents confirm (muṣaddiq) that which is “with” the audience. Since this verse is addressed to the People of the Book, the reader could reasonably assume that it has the Torah and/or Gospel in mind (see 3.3). For an analysis of this claim of confirmation, and a response, see the comments at 46.12.