Archangel Gabriel and the Revelation

Why could other people who were in close vicinity to the Prophet not see Archangel Gabriel when he was delivering the Revelation to
the Prophet?

There are living creatures as well as sounds that exist in different dimensions of the universe. We, as human beings, are capable of seeing, hearing or perceiving only some of these. There are, for instance, thousands of sounds and species around us that we have never heard or seen. Our being totally unaware of them does not mean that they do not exist. Moreover, we are able to see certain species only with the help of special devices, for instance, microscopes. Likewise, the one who delivered the Revelation to the Prophet was an angel, and the angels are luminous, spiritual creatures, invisible to the human eye. It is impossible for us to be aware of them with our senses. It was possible, however, for people to witness certain manifestations of the Revelation while the angel was delivering it to the Prophet; when the Companions were in the presence of the Prophet they were occasionally able to witness such manifestations and thus knew that the Prophet was receiving a Revelation.

 

Akgul, Muhittin (2009). The Quran in 99 Questions (Abdullah Erdemli Trans.). New Jersey: Tughra Books. (Originally published in Turkish as Kur’an İklimine Seyahat)