My Fair Lady (1964)

Loved it. 

I think what really provides the "heart" of the story is the strong message about the value of a person, shown through the relationship between Eliza and Henry.

Eliza Doolittle

Eliza has only ever wanted to be acknowledged and respected for who she is. She knows she's a good person and just as worthwhile as anyone else, and isn't afraid to let people know. The gap in social status is simply a matter of bad luck; she just happens to not have any money.

Eliza: "I'm a good girl, I am!"

Henry Higgins

Henry Higgins, believes that a person's status and worth is determined by their behavior, in particular the way they speak. He sets out to prove his point by passing off Eliza as royalty, citing her as an ideal candidate.

Higgins: "She's so deliciously low, so horribly dirty. "

As they enter into their teaching arrangement Eliza believes, as Henry suggested, that if she can learn to act like a lady, people will see her for who she is. Henry believes by training her to act like a lady, he will have created a new and better person.
At first this isn't a problem, but once Eliza's training is complete the subtle difference in their beliefs comes to light.

Higgins: "By George, I really did it, I did it, I did it! I said I'd make a woman and indeed, I did."

Eliza: "what's to become of me? . . .  I sold flowers; I didn't sell myself. Now you've made a lady of me, I'm not fit to sell anything else. " 

As Eliza walks out on him, Higgins is baffled. He admits that he doesn't want her to leave, but can't understand why she won't just behave rationally - like a man. Eliza, with her new-found powers of articulation, explains things all too clearly:

Eliza: " . . . the difference between a lady and a flower girl is not how she behaves, but how she is treated. I shall always be a common flower girl to Professor Higgins, because he always treats me like a common flower girl, and always will. But I know that I shall always be a lady to Colonel Pickering, because he always treats me like a lady, and always will."

This ties their argument into the overall theme and Higgins is forced to re-evaluate his position. Even though it's not directly presented in the film, I think the underlying message is clear:

Higgins learns that the problem is not that Eliza refuses to act like a respectable person, rather that he has refused to treat her like one.