The Manifestation of Losses - 64:6 "Because their messengers went to them with clear proofs and they said, "Shall a man show us the right way?"So they disbelieved and turned away. Allah is not in need of anything. Allah is the Rich, the Praised."
Why a human messenger?
The Bee/16:43 We did not send before you as messengers except men, those who walked on two feet, and We revealed to them. Ask the experts if you do not know.

The Prophets/21:7 We did not send before you any messenger except to men, but We revealed to them; ask the experts if you do not know.

Prophet Joseph/12:109 We did not send before you except men whom We revealed to you from among the inhabitants of the cities. Do they not travel through the earth and see the fate of those before them? Is the abode of the Hereafter better for the righteous; do you not understand?

The Pilgrimage/22:75 Allah chooses messengers from angels and mankind. Surely Allah is All-Hearing, All-Seeing.

The Night Journey/17:95 "Say: "If there were angels inhabiting the earth, We would have sent to them an angel from heaven as a messenger."