a certain - an extraordinary and indescribable. The indefiniteness, as of something peculiar of its kind, makes the description the more terrible (compare Greek, Jam 1:18).
looking for - “expectation”: a later sense of the Greek. Alford strangely translates, as the Greek usually means elsewhere, “reception.” The transition is easy from “giving a reception to” something or someone, to “looking for.” Contrast the “expecting” (the very same Greek as here), Heb 10:13, which refutes Alford.
fiery indignation - literally, “zeal of fire.” Fire is personified: glow or ardor of fire, that is, of Him who is “a consuming fire.”