(Is it a wonder for mankind that We have sent Our revelation to a man from among themselves (saying): "Warn mankind, and give good news to those who believe that they shall have with their Lord the rewards of their good deeds" (But) the disbelievers say: "This is indeed an evident sorcerer!") (10:2). And Allah says here:
The background of the revelation of the initial verses of this Surah was that Abu Talib, the uncle of the Holy Prophet ﷺ was doing his best as his guardian, despite that he had not yet embraced Islam. When he fell sick, the chiefs of the tribe of Quraish held a consultative meeting in which Abu Jahl, ` As Ibn Wa'il, Aswad Ibn Muttalib, Aswad Ibn ` Abd Yaghuth and several other chiefs participated. They discussed the situation they faced. Abu Talib was sick. If he were to pass away and they were to take some strong action against the Holy Prophet ﷺ to restrain his activities in favor of promoting his new faith, the people of Arabia will throw taunts at them and say, 'Here are these people who could do nothing against him while his uncle Abu Talib was alive while, now when he has died, they have stood up against him as their target. So, they came to the conclusion that they should decide this thing about Muhammad ﷺ while Abu Talib was still alive, so that he would stop speaking ill about their objects of worship.
The Prophet Muhammad is a great name today, because subsequent history has glorified him. But when, in the seventh century A.D. he announced his prophethood, it was difficult for people to believe that this ordinary-looking person was chosen to receive God’s revelations. It is crucial to understand that once history has taken shape, even a blind man can recognise a prophet, but before history takes shape immense sincerity is required to acknowledge a prophet. The exceptionally different style of the Quran used to stun its opponents, but the ordinary image of the bearer of the Quran would cast them into doubt. Bent on rejecting him, these people used to denigrate the Prophet in various ways, called him a magician or a liar. They could not reconcile themselves to the possibility of their great men being in the wrong as against an ordinary man.
Uthmani text of the Madinah mushaf (King Fahd Complex). Translation: Saheeh International. Tafsir via Quran.com.