This troper spent a good fifteen minutes after the show speculating what they meant by the phrase, "I may not have been changed for the better, but, because I knew you, I have been changed for good," until said troper realized 'for good' was used in the sense of permanence.
Glinda's "The Wicked die alone" is, of course, completely inappropriate (and a cover-up), regarding Elphaba - but totally appropriate regarding Madame Morrible. This troper guesses that's how Glinda was able to sing it with the straight face.
She doesn't know it's a cover-up. She watches Elphaba melt behind the curtain, and picks up her hat and bottle, the only things apparently left of her.
And it's appropriate for herself: Glinda has reasons to blame herself for the death of Elphaba, Fiyero, and Nessarose, and the dehumanization of Boq, and she's lost everyone she had a real connection to. "The wicked die alone."
Similarly, Glinda says "Isn't it nice to know that good will conquer evil. The truth we all believe'll by and by outlive a lie for you and-" She's cut off by an Ozian, indicating that she doesn't really believe the cover story.
Glinda also sings, "Let us rejoice-ify that goodness can subdue/the wicked workings of...You-know-who." By the end of the play I realized that she was not singing about Elphaba(whom she didn't regard as wicked), but about the Wizard and Madame Morrible, the real villains of the play.
The songs have some excellent examples of Fridge Brilliance as well. It took this troper about fifty times hearing "What is This Feeling" before he realized that "Blonde" actually rhymed with "Respond" from several lines back; ditto for the sneaky extra rhyme snuck into this segment of "Dancing Through Life" (note the italicized words):
Boq:Uh, Nessa? I've got something to confess, a...
One of the best hidden rhymes, though, is in "Popular". The line "I remind them on their own behalf", which sounds almost like an orphaned line, is actually separated from a sneaky matching rhyme by almost fifteen seconds.
Towards the end of "One Short Day," when Glinda sings, "Two best friends," you can hear a little chime that matches "ev'ry little trait" from "What Is This Feeling?" Shout Out for the win!
Tiny bit of Les Yay in a similar sequence: The first time we here the tune from "I'm Not That Girl" is at the end of "Popular" when Glinda tells Elphaba that she's beautiful.
This troper interpreted it differently. "I'm Not That Girl" as both a song and a refrain touches on feelings of inadequacy. I saw it as Elphaba looking into the mirror and realizing she's still green and not (conventionally) attractive. But anyhow, the ambiguities in this musical make it fun :)
Over the course of the musical, various phrases involving the word "good" are used — "making good", "thank goodness", "for goodness' sake", etc. — and as these phrases are overused by characters who are anything but "good", the word gradually loses all meaning . . . until the end, when the song "For Good" uses it with a different definition from the rest of the show, and it becomes meaningful once again.
The: "You're beautiful." "Don't lie to me." "It's not a lie, it's just looking at something a different way." exchange that is repeated at the end doesn't only sum up Fiyero and Elphaba's relationship. It essentially sums up the main theme of the musical.
Elphaba makes several obvious prophetic statements in "The Wizard And I" ("Someday there'll be a celebration throughout all of Oz/That's all to do with me", "I'll be so happy I could melt", "When people see me they will scream"). However, she also makes a less obvious one at the end of "Defying Gravity": "And nobody in all of Oz/No Wizard that there is or was/Is ever gonna bring me down!" The person who ultimately brings Elphaba down (at least in the eyes of the public) is Dorothy, who is from Kansas and possesses no inherent magical abilities.
When Elphaba casts a spell to save Fiyero's life in "No Good Deed", she declares "And however they try/To destroy him/Let him never die/Let him never die." In addition to making Fiyero indestructible, she also made him immortal.
Sorcery has enough of an intellectual foundation that they actually teach classes on it at Crage, yet somehow the field is still so underpopulated that when the Wizard needs talented mage types to help him rule Oz he sends Madame Morrible to a boarding school in order to act as his talent scout.
...Not to mention the fact that he seems to be scouting only at Crage Hall, which might indicate that none of the boys' schools teach sorcery. For some reason.
He was searching for amazing power and potential. If a person doesn't have power or potential (i.e. the Wizard) then all that education is useless. The potential has to be there first. The learning can come later. By searching for students with magical potential, they can find a powerful witch and have a degree of control over her. Don't know about the women thing... Females have babies and therefore have more life-force? Maybe cultural roles make men warriors and women magic-users?
Sorcery might have a decent foundation, but there aren't very many who are actually good at it—look at Glinda's professor, who is described as virtually incompetent. As for Madame Morrible being only at Crage Hall...maybe he has other scouts with the boys, but because none of the male characters study sorcery, they don't know.