Why was "those who disbelieved" used instead of "the disbelievers" or "the infidels" in the verse: "Indeed, those who disbelieved – it is all the same for them whether you warn them or do not warn them – they will not believe"?

The noble verse was placed in its context with the best and clearest wording, and this is one of the manifestations of the Qur'an's miraculousness. The aforementioned verse was separated from the preceding sentence and was introduced by the emphasizing particle "إن" (indeed), followed by the relative pronoun "الذين" (those who); this was for the complete discontinuity between the two sentences, to emphasize the news, and to refer to a specific group of disbelievers from Mecca whom Allah knew would not respond to the Messenger. Ibn Ashour mentioned that this verse is a transition from praising the Book to speaking about those who are not guided by it, because their deprivation from guidance was due to the wickedness of their own souls.