Character Analysis
British Nanny Airways
After Mary Poppins flies away on her umbrella at the movie's end (Southwest Airlines was apparently booked, and an umbrella is cheaper anyway) we're left wondering: who or what is Mary Poppins?
Is she a witch? "No," says Michael Banks, "witches have brooms." A superhero, then? That makes more sense, but she doesn't have a uniform. Is she…a god (or goddess)? Actually, P.L. Travers said that the version Mary from the books seemed kind of like the Hindu goddess Kali. (Source)
Whatever the case, Mary's got some serious supernatural powers. She's not like other people—as her magical measuring tape says, she's "practically perfect in everyway." So, whatever Mary is, she's a good 'un.
But she's not a dynamic 'un—Mary isn't really a character who changes or goes through a struggle. She's in control. Called down from her perch atop a cloud by the Banks children's torn up advertisement for a new nanny, she starts setting things right in the Banks house. She never gets ruffled and doesn't run into any obstacles that perplex her. Mary knows what she's doing.
Basically, she's a benevolent force, who arrives to make the children's father pay more attention to them. George Banks has become a workaholic, treating the rest of his world as though it were the same as the bank he works at. By becoming the children's nanny and taking them on wild adventures, Mary is acting as a positive role model for George. She's making him jealous—and making him want to be more like her at the same time.
We don't know where Mary comes from, or why she does what she does. Apparently, she's helped other children and parents with their problems too. And, somehow, she knows Bert the cockney chimney sweep—they have a romantically ambiguous relationship (Bert seems to have the hots for Mary, but it's not totally clear).
Her Uncle Albert lives in London, so she might be a local in some sense. She has a proper British accent, at any rate. Also, she must have a life of her own, since she gets Tuesdays off.
Dropping Knowledge
Mary's philosophy is pretty simple, but it's also effective. She cuts right to it early on in the movie:
MARY: A spoonful of sugar helps the medicine go down.
There are oceans of meaning hidden in this simple phrase. According to Richard Sherman—half of the songwriting duo who penned the number—it captures "the whole essence of the movie—which was about the power of love." (Source)
By showing kindness to the children, Mary's giving them that "spoonful of sugar," and showing Mr. Banks how to do that too. He loves his children, but has forgotten how to show it…
But the "spoonful of sugar" isn't only about parental love. It's also about learning how to let loose and enjoy life. Mary transforms cleaning up the nursery into a fun task, by adding magic, making what would be totally boring into something cool:
MARY: In every job that must be done, there is an element of fun. You find the fun, and—snap—the job's a game!
(Then again, since you can't actually clean up a room with magic, how do you find "the element of fun"?)
Mary doesn't teach these lessons to Mr. Banks by lecturing him—she does it through example. Sometimes, this can end up being pretty baffling. After Mary Poppins leads a bunch of chimney sweeps through the room—at the end of the "Step In Time" musical number—Mr. Banks wants her to explain herself. She says:
MARY: First of all, I would like to make one thing quite clear.
GEORGE: Yes?
MARY: I never explain anything
Mary is almost like a Japanese Zen Master (to cite another example from Travers). She teaches through bafflement and awe. (Source)
Family Psychologist
Mary also orchestrates the incident that sets off the movie's climax and force Mr. Banks to change. Banks' jealousy has gotten so intense that he wants to fire her, but Mary acts like she's on his side, saying he should teach the children discipline by taking them to the bank. She sings a song to Jane and Michael about an old lady who feeds pigeons and sells bags of seeds for a tuppence a piece:
MARY: Feed the birds, that's what she cries, while overhead her birds fill the skies. All around the cathedral the saints and apostles look down as she sells her wares. Although you can't see it, you know they are smiling each time someone shows that he cares. Though her words are simple and few, listen, listen, she's calling to you. Feed the birds, tuppence a bag. Tuppence, tuppence, tuppence a bag. Though her words are simple and few, listen, listen she's calling to you. Feed the birds, tuppence a bag. Tuppence, tuppence, tuppence a bag.
She apparently knows the future, or at least the geography of London, since the children actually see the pigeon lady the next day, and Michael wants to use his tuppence to feed the birds.
At the bank, this causes a row with the head of the bank, Mr. Dawes, who tries to force Michael to put his tuppence in a savings account, which causes Michael to fight to keep his tuppence…which causes a run on the bank. And that causes Mr. Banks to get fired, which makes him realize that his family's what's truly valuable.
And Mary Poppins was the kind-hearted puppet master behind this whole fiasco.
Mary flies away when the wind changes, leaving a happy Banks Family behind. Her work there is done. Of course, Mary can't help getting attached to the kids, as her talking umbrella points out—but, she knows that their father's replaced her role in the family, which is as it should be.
So, she launches off on her umbrella, still "practically perfect," and ready to help some other family get its act together. She's like a talk show psychologist…except, you know, actually effective.