This is the first major chapter that interrupts the "plot" of the novel in order to discuss whaling in general. Don’t tune out, though: some of Melville’s best jokes are in these chapters.
Ishmael becomes a kind of advocate for whaling as an activity. He argues that whaling is a worthwhile profession and not an "unpoetical and disreputable pursuit" (24.1), as some people argue.
Ishmael establishes that whaling isn’t respected as a profession: you couldn’t have a calling card in high society that says you’re a harpooneer, he points out.
The first reason people object to whaling is that it seems like butchery. Ishmael admits that it is, but argues that military service is much bloodier and involves more bloodshed, and it’s considered honorable.
Ishmael reminds the reader that many of the lamps and candles in the Western world are (at this point in time, the mid-nineteenth century) made with whale oil and whale blubber.
Ishmael tells the reader some whaling history and statistics, showing that whaling has been respected and honored by kings—and that it’s really very profitable.
Ishmael also claims that, over the past sixty years, whaling has made the world a lot safer. For example, according to Ishmael, whaling ships were the first to go to many distant countries and establish relationships with unknown peoples.
Ishmael then brings up a series of aesthetic objections to whaling that he proceeds to shoot down:
If you argue that there aren’t any famous epic stories about whaling? Ishmael answers with the book of Job, the writings of Alfred the Great about a Norwegian whaler, and a speech made in Parliament by Englishman Edmund Burke referencing whaling.
If you argue that whalemen aren’t noble? Ishmael snaps back that Benjamin Franklin is distantly related to a whaling family.
If you argue that whaling isn’t respectable? Ishmael points out that the whale is called "a royal fish."
If you argue that the whale "never figured in any grand imposing way"? Ishmael hits you with a famous Roman procession that involved the bones of a whale.
If you argue that there is "no dignity in whaling"? Ishmael gets in a constellation in the south called Cetus (the whale). What’s more, Ishmael respects Queequeg, and those who can kill whales more generally, more than any king or general who has stormed human towns.
Finally, Ishmael says that, if there is any value in his own behavior or in his manuscript, he’ll give all the glory to whaling, because it has taught him everything he knows.