(Verily, We have inspired you...) emphasized the Prophet's prophethood and refuted the idolators and People of the Scripture who denied him. Allah said,
لَّـكِنِ اللَّهُ يَشْهَدُ بِمَآ أَنزَلَ إِلَيْكَ
(But Allah bears witness to that which He has sent down unto you,) meaning, even if they deny, defy and disbelieve in you, O Muhammad, Allah testifies that you are His Messenger to whom He sent down His Book, the Glorious Qur'an that,
Then comes verse رُّسُلًا مُّبَشِّرِينَ وَمُنذِرِينَ (-- Messengers giving good tidings and warning...) which succinctly tells that Almighty Allah consistently sent messengers to convey good tidings to all believers and to warn all disbelievers so that there remains no room for the excuse that they did not know the will of God and His Messengers --had they known about it, they would have certainly followed it! Now, that Almighty Allah has sent messengers with miracles and His messengers have shown the straight path of truth, the option of not accepting the true faith cannot be accepted from anyone, under any pretext or excuse. Such is the nature of Divine Revelation. Wahy is an absolute argument, final, conclusive and disarming. No argument stands operative against it. In fact, all arguments lie surrendered under its weight. And this is the wisdom of Allah and His modus operandi.
However, according to the requirements of the age, different prophets received different kinds of succour from God. This is still how God functions, so that those of his servants who came forward to spread His message will likewise, according to their circumstances, receive special divine succour, in order that they may effectively continue to carry out their dawah responsibilities. At the time when the Prophet Muhammad was chosen as a Messenger by God, the Jews enjoyed the status of representatives of the divine religion. For their part, they had supposed themselves to be the chosen people, the sole custodians of divine religion. As such, they occupied all the religious positions of honour. Not wishing to acknowledge any other’s greatness save their own, they refused to believe that the Arab prophet had been sent by God to communicate His message to mankind. They thought that they had a monopoly over religion; that, if they did not testify to a person’s being a representative of God, he would lack all credibility. They had forgotten that this was God’s universe, its system tended by God’s obedient angels. Thus the real validation comes from God, and is supported by the entire system of the universe. Indeed, it is God, with His entire universe, who supports His messenger, rather than someone’s self-styled suppositions.
Uthmani text of the Madinah mushaf (King Fahd Complex). Translation: Saheeh International. Tafsir via Quran.com.