For Captain Vere, order is everything. If the Indomitable is to achieve a successful voyage, good order among the crew must always prevail. And as Vere is captain of the ship, that onerous responsibility falls upon his shoulders. He loved Billy dearly, but when it comes to doing his duty as captain, Vere's feelings simply don't enter into the equation. If Captain Vere were to show lenience to Billy, then he'd be setting a very dangerous precedent indeed. Sailors throughout the British navy would see it as a green light to challenge authority, and that's not something that Vere, or any other ship's captain, should ever be prepared to tolerate.

In the above quotation, what Vere is saying is that custom or habit, not emotion, governs our behavior. This is especially true of professionals involved in dangerous occupations such as sailors, who need to adhere to the "measured forms" of the Mutiny Act if they're to maintain good order on the high seas.

This remarkable story and play by Herman Melville again uses the sailor's life as its setting.  Here, however, instead of a whale as the antagonist, the unquestionable rule of law is the "beast" attacking human desires.  Billy Budd is a good person in every respect; yet, according to the immutable laws of the sea (a microcosm of all society), Capt. Vere is right in condemning Budd.  This is what Vere is referring to in this quotation. He is underlining his belief that "form" supercedes "substance", that human compassion is not sufficient excuse to break the "formal" structure, a structure that is the underpinning of a civilized society (and certainly a necessity in the tightly closed, and inescapable "society" of a ship at sea).  An interesting side character is Dansker, who, being Danish, represents the universality of social order.