Prophet Hud - 11:31
I do not say that the treasures of Allah are with me, nor do I know the secret, nor do I claim to be an angel, nor do I say that Allah will not grant any favor to those whom your eyes despise. Allah knows better their secret thoughts. Otherwise I would be of the wrongdoers.
Why a human messenger?
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."