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."
Among the main characters who are Shiz students, isn't it interesting that the one known as Glinda the Good planned a successful murder (dropping a house on Nessa), while the ones with salacious reputations - Elphaba the Wicked Witch, and Fiyero the brainless prince - never did anything evil? So Glinda is the only evil one. No One Mourns the Wicked is sung by her, and for her.
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.
This troper thought the ending of a line in "Popular" when Glinda adds "-lar" was a joke about having to adjust the pronunciation for a rhyme. It's actually rhyming the double ending of a line before it.
I KNOW ABOUT POPULAR
AND WITH AN ASSIST FROM ME
TO BE WHO YOU'LL BE
INSTEAD OF DREARY WHO-YOU-WERE... ARE...
THERE'S NOTHING THAT CAN STOP YOU
FROM BECOMING POPU-
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.
Glinda's line in "What is this Feeling?" in her letter to her parents states that "Of course, I'll rise above it" in regards to her current roommate situation with Elphaba. What makes this brilliant is that in the end, she must do this both literally and metaphorically. While in her bubble, she literally can "rise above" Elphaba. From a more symbolic standpoint, it describes how she must become the changing influence that Elphaba never could be (as described in "For Good") as she moves on from Elphie's "death"..
The Wicked Witch of the West's death scene in the original film, with the overwrought "Oh, what a world! What a world!" and all that, makes much more sense if you realize that Elphaba was deliberately being overdramatic to add weight to her faked death.
Two characters are referred to as "wonderful", the Wizard (his title, "The Wonderful Wizard of Oz" and Boq ("Oh, Boq, I think you're wonderful!" sung by Nessarose). Both lie about their true selves - the Wizard is only "wonderful" because the Ozians made him so, Boq is only "wonderful" in Nessa's eyes because Glinda manipulated him.
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.
As "For Good" states, both Elphaba and Glinda have changed each other. Had it not been for that and the strength of their friendship, things would have gone much differently. Elphaba was used to being seen as an abomination, but it was knowing that Glinda was still on her side gave her hope that she could return once she had stopped the Wizards plan. Glinda was used to being well loved, and the character development from seeing how she was hurting Elphaba and could actually do something about it gave her the ability to work from the inside to fix the corruption. Had they not become friends, Elphaba's desire to be accepted would have made her capitulate to the Wizard's wishes from the beginning.