“Tell them (O Prophet!): ‘Then do bring a Book from Allah which is a better guide than either of them, and I will follow it! Do so if you are truthful!’ But if they do not hearken to this, then know well that they only follow their lusts and who is in greater error than he who follows his lusts without any guidance from Allah? Allah does not guide those given to wrong-doing. We have constantly conveyed them the word (of admonition) that they may take heed. Those to whom We gave the Book before do believe in this.”
(Al Qur’ān – 28:49-52)
As far as exhorting people to follow the Truth was concerned, the Qur’ān had done all that was needed. Only those who can eschew stubbornness and who are ready and willing to accept the Truth are guided by it.
The ayat 28:52 does not mean that all the People of the Book – the Jews and the Christians – in fact believe in it. It actually refers to a particular incident which took place at the time this surah was revealed and which was meant to jolt the Makkans into making their ingratitude known. And that incident was: God had done them a great favour by raising someone from among them as a Prophet. Their rejection of him was their shame. Conversely, those from far-off places outside Makkah were making their way to the city, recognising as they did the true worth of the Prophet ﷺ from whom they derived immense benefit.