Why was "a world" used in this sentence of Melville?

Question

I cannot make much sense of "a world" in the following passage from Moby-Dick:

There’s your law of precedents; there’s your utility of traditions; there’s the story of your obstinate survival of old beliefs never bottomed on the earth, and now not even hovering in the air! There’s orthodoxy!

Thus, while in life the great whale’s body may have been a real terror to his foes, in his death his ghost becomes a powerless panic to a world.

Methinks Melville referred to the existing world he knew (the world of "traditions", of "old beliefs", of "orthodoxy") and not to an imaginary word (when referring to such a non-existing world the indefinite article is frequently used). Therefore, the definite article would make more sense to me in this sentence, like so:

Thus, while in life the great whale’s body may have been a real terror to his foes, in his death his ghost becomes a powerless panic to the world.

Would such sentence be incorrect in the context of the passage in question? Why was the indefinite article chosen by Melville?

Answer 1

Since this question was moved over from English Language stack, I'll repost my answer from there, for posterity, if not vanity.

All the answers [there] so far focus on the meaning of the word "world", ignoring the contrasting context in which it was used in the original sentence. I believe "a world" puts emphasis on the difference between a narrow and a wide influence the whale has; on "his (immediate) foes" and "a (whole) world". In life, the whale only terrified his would-be attackers, while in death its ghost terrifies everyone whoever hears of its story. The "world" is thus a measure of reach, as in, "a person, a family, a country, a world".