As for the likeness of the living creatures, their appearance was like burning coals of fire, and like the appearance of lamps: it went up and down among the living creatures; and the fire was bright, and out of the fire went forth lightning.
As for the likeness ... their appearance - not tautology. "Likeness" expresses the general form; "appearance," the particular aspect.
Was like burning coals of fire - denoting the intensely pure and burning justice wherewith God punishes, by His angels, those who, like Israel, have hardened themselves against His long-suffering. So in Isaiah 6:1-13 (if the seraphim be the same as the cherubim), instead of cherubim, the name "seraphim," the burning ones, is applied, indicating God's consuming righteousness; whence their cry to Him is, "Holy, holy, holy!" and the burning coal is applied to his lips, because the message through his mouth was to be one of judicial severance of the godly from the ungodly, to the ruin of the latter.
Like the appearance of lamps - torches. The fire emitted sparks and flashes of light, as torches do.
It went up and down - "it" - i:e., the fire went up and down, expressing the marvelous vigour of God's Spirit in all His movements, never resting, never wearied.
The fire was bright - indicating the glory of God.
Out of the fire went forth lightning. God's righteousness will at last cause the bolt of His wrath to fall on the guilty, as now on Jerusalem.