Tone in The Importance of Being Earnest
Lane lies in order to cover for his employer, who has eaten all of the cucumber sandwiches already. This ability to lie and think on his feet suggests that, though Algernon isn't interested in Lane's personal life or his personality, Lane himself knows Algernon very well and is able to lie for him in front of (the very shrewd) Lady Bracknell without even batting an eye. This isn't necessarily a characteristic Lane embodies outside of work, but it certainly suggests that he's good at his job.
Wilde has spent a considerable amount of time building up Cecily's diary, telling us what she writes in it, why she insists on it, and how it differs from the writing of, say, Miss Prism. Given all this build-up, it's reasonable for the audience to expect that the diary will be brilliant, or at the very least interesting. Instead, it's flat and spiritless, giving us only the barest factual account of her day: what happened, what the weather was like. Wilde deliberately falls short of our expectations here for comedic effect.
Miss Prism gently mocks the Chasuble, mirroring the structure of his earlier statement ("my metaphor was drawn from bees") and building on its sexual overtones by referring to women as either ripe or green (unripe). This metaphor suggests that a young woman like Cecily, for instance, can't always be trusted, but an older, more mature woman like Miss Prism certainly can be (and wants to be).
Jack uses understatement to express his supreme displeasure with Lady Bracknell and their entire conversation. In point of fact, Cecily has inherited a large sum of money, and Jack knows very well that it will change Lady Bracknell's mind about the engagement, but he tells her about it in such a perfunctory way so as to make her ideas about money and social status seem all the more shallow.
Wilde uses this line to indicate that a beat has passed without having to rely on stage direction to tell the actors and the audience that time has passed and that this silence has been painfully awkward for both of them. Wilde often uses his tone and diction to substitute for stage direction, which makes it easier for the reader to imagine the voices and facial expressions of these characters without having to see the play. This is part of the genius of Wilde's work.