Commentary
Verse 69 exposes the cherished desire of the people of the Book to mislead Muslims away from the true faith they are on. The text, then, firmly declares that the victim of their effort to misguide is no one other than themselves, something they do not realize.
Verse 70, addressing the people of the Book, asks them as to why they disbelieve in the signs of Allah, such as the verses in Torah and Injil which prove the prophethood of Muhammad ﷺ because the denial of his prophethood amounts to declaring these verses to be false which is infidelity, although they themselves confirm these as true. This is an admonition on their error in belief.
Proceeding further, Verse 71 admonishes them for confusing the real statement, that is, the prophecy about the prophethood of Muhammad ﷺ with the fictitious, that is, the interpolated statements or false exegesis. The crucial question being asked is as to why would they conceal the truth of the matter despite knowing the truth, and knowing that they are hiding it.