Surah 17. Al-Israa, Ayah 95

The argument is that if angels inhabited this earth, an angel from heaven could be sent down as a messenger to them, as they could mutually understand each other, and the Message of Allah could be explained without difficulty. But the earth is inhabited by men, and the men themselves are divided into races, or groups, or nations. To each Group is sent a prophet from among their brethren: to 'Ad, their brother Hud (xi. 50); to Thamud, their brother Salih (xi. 61): and so on. As a matter of fact, with wicked men, constituted as they are, the appearance of an angel causes disturbance and an unseemly riot, as in the case of the angels that came to Lot (xi. 77-80). In any case they cannot carry out an effective mission among men (vi. 8-9).