Surah Al-An'am — Ayah 9 (6:9)
وَلَوۡ جَعَلۡنَٰهُ مَلَكٗا لَّجَعَلۡنَٰهُ رَجُلٗا وَلَلَبَسۡنَا عَلَيۡهِم مَّا يَلۡبِسُونَ ٩
English translation (Saheeh International)
And if We had made him [i.e., the messenger] an angel, We would have made him [appear as] a man, and We would have covered them with that in which they cover themselves [i.e., confusion and doubt].
Brief commentary
If I had sent an angel to them, I would have made him in the form of a man, so that they could listen and learn from him, as they would not be able to learn from an angel in the original form that I created him. If I had made him in the form of a man, they would have been confused about him.