While spending the night at Wuthering Heights, Lockwood peruses the titles of some old religious books next to his bed and proceeds to dream about one of the authors, a preacher named Jabes Branderham. The dream (really a nightmare) is a satire of lengthy sermons by English Nonconforming ministers:
However, in my dream, Jabes had a full and attentive congregation: and he preached—good God—what a sermon! divided into four hundred and ninety parts—each fully equal to an ordinary address from the pulpit—and each discussing a separate sin! Where he searched for them, I cannot tell; he had his private manner of interpreting the phrase, and it seemed necessary the brother should sin different sins on every occasion.
The title of Branderham's actual sermon is "Seventy Times Seven, and the First of the Seventy First." The title alludes to a passage in the Gospel of Matthew, where Peter asks Jesus how often we should forgive "a brother" who sins against us—up to seven times? Jesus replies that we should rather forgive "seventy times seven" times, a clear hyperbole meaning that Christians should always be willing to forgive. In Lockwood's dream, however, Branderham takes the "seventy times seven" literally, dividing his sermon on the subject into 490 sermon-length sections—meaning that Lockwood is nightmarishly cursed to listen to 490 consecutive sermons. Not only that, but Branderham devotes each sermon to a different kind of sin.
Brontë expects her audience to find Lockwood's dream funny because of its satirical take on real-life sermons by English Nonconforming preachers. "Nonconformist" simply refers to Protestants who weren't part of the officially established Church of England (Anglican)—groups like Methodists, Baptists, and Quakers, among others. By the time Wuthering Heights was published in 1847, there were more Nonconformist chapels and meetinghouses than Church of England churches in England. (Also, note that Brontë's father was an Anglican curate.) Nonconforming ministers were often known for their lengthy sermons, which were broken into minute divisions—though Branderham's 490-part discourse is pure exaggeration. Branderham's insistence on delineating 490 distinct sins is also a satiric reference to some Nonconforming preachers' idiosyncratic interpretations of the Bible, and perhaps especially to their tendency to come up with more and more kinds of sin to preach against.
Though Nonconformist sermons, both written and preached, were very popular, plenty of drowsy listeners no doubt wished they could respond as Lockwood ultimately does in the dream—by exploding with frustration at the tireless preacher. Though this satirical dream doesn't serve much of a narrative purpose beyond setting up Lockwood's next nightmare, it is probably meant to give readers a good laugh and a moment of levity before the story takes a darker, more Gothic turn.