In the days when I was sitting in his class, he omitted so many needless words, and omitted them so forcibly and with such eagerness and obvious relish, that he often seemed in the position of having shortchanged himself—a man left with nothing more to say yet with time to fill, a radio prophet who had outdistanced the clock.
Source: Steven Pinker: Sense of Style, pp. 1–2.
Can you please explain to me what the bold passage from the above excerpt means. I am not really able to find the meaningful interpretation of that. The literal reading does not make any sense to me.