Ishmael describes the first mate of the Pequod, Starbuck. (However, we’ve got to note that, at this point in the novel, the distinctive story-telling voice of Ishmael is fading further and further away as the narrator seems to become Melville himself.)
Starbuck is a Nantucket Quaker, and he’s basically the goody-two-shoes play-by-the-rules do-it-by-the-book officer on the ship.
Starbuck’s most striking physical characteristic is his leanness—he seems tight, dry, and condensed, and looks like he could endure terrible weather.
Personally, Starbuck is "steadfast" and conscientious (26.1); he’s also a little bit superstitious, but in an intelligent way.
He wants all his sailors to be afraid of whales, because men who respect the power and danger of the whale will be better companions than cocky guys who take stupid risks.
Starbuck is also a reasonable and pragmatic fellow; he’s brave, but always weighing the pros and cons of behaving bravely in any particular situation. He’s not one for extreme risks.
Still, Ishmael can tell that there’s some deep flaw in Starbuck that could break him and ruin all his courage.
Ishmael (or perhaps the speaking voice is Melville) assures the reader that Starbuck isn’t going to be completely broken in the course of the novel. That would violate the essential dignity of man in some way.
The narrator (Ishmael or Melville) explains that, if he’s going to exalt and glorify men who seem lowly, then that’s just the result of the democratic equality of men.
After all, men like John Bunyan (the author of A Pilgrim’s Progress, who was a convict), Miguel de Cervantes (the author of Don Quixote, who was disabled and a pauper) and Andrew Jackson (the seventh president of the United States, who grew up poor) have been glorified by history.