Above the firmament; the crystalline firmament which appeared in the vision, not the vast expanse or firmament in which are sun, moon, and stars.
That was over their heads; heads of the living creatures which moved the wheels, and stood by the chariot.
Was the likeness of a throne, as the appearance of a sapphire stone; in view appeared a sapphire stone, like or in likeness of a throne; so the Hebrew, though we transpose the words somewhat in our version: the sapphire speaks splendour and preciousness; the throne speaks the authority and power of him who sitteth thereon.
As the appearance of a man; Christ, God-man, who here appears as King and Judge to vindicate his own honour, to punish rebels, and to give warning by his prophet ere he execute his just but severe indignation.