Overall meaning : Allah, Glorified and Exalted be He, states that even if He were to send down to His Prophet, Muhammad, may Allah bless him and grant him peace, a book written on paper and they touched it with their own hands, the unbelievers would still persist in their obstinacy and say it is nothing but manifest, downright magic. They would also say, in their continuing stubbornness, 'Why has an angel not been sent down to Muhammad to support him and testify to his truthfulness and credibility?’ In response to this, He states that had He sent an angel to them, just as they demanded, He would have hastened their punishment if they still refused to believe, and they would not have been given a respite or chance to repent.
The Almighty then affirms that it would be pointless to send them an angel. Had He sent an angel, Allah asserts, to confirm Prophet Muhammad’s claim and credibility and to command them to follow him, He would surely have given such an angel a human form so that they would be able to understand him and thus benefit from his teachings as they cannot possibly see an angel in his true form. Sending them an angel in human form, however, will cause them confusion as to whether he is human or an angel, just like the confusion they have caused themselves over accepting the message of a human messenger by ruling out the fact that the messenger would be human like them.
Then, addressing His Prophet, Muhammad, may Allah bless him and grant him peace, He explains to him that nations before him also mocked their messengers, and so He punished them for deriding them and instructs him to say to those who disbelieve him: Travel in the land and pause to contemplate the ruins left behind by the past nations who disbelieved their messengers, see how they were doomed to destruction along with their dwellings and take warning from their example.