"It's considered one of the seminal movie musicals, and also the third most notable Judy Garland movie."
If remembered for nothing else, Meet Me in St. Louis is the film in which Judy Garland introduced "Have Yourself a Merry Little Christmas." After a slow start, around the 80s it became a top ten Christmas song on every singer's Christmas album. In 2007 ASCAP ranked it as the third most performed Christmas song in the previous five years.
In the 50s, gas stations distributed records containing a sampler of popular Christmas songs, like the Boston Pop's "Sleigh Ride." I was just a kid and my mother would play the record a lot. I knew nothing of Judy Garland or Meet Me in St. Louis, but I was entranced by "Merry Little Christmas" because of the achingly heartfelt performance by Garland. In the film Garland sings this to her young sister Margaret O'Brien, and it is a sad occasion because Papa is going to uproot the family from its happy home in St. Louis and move to big, bad New York.
Probably the song didn't become a wildly popular Christmas song until the lyrics were changed to make it more generic, and less specific to the film (although hard line old-timers like Mel Torme stuck to the original lyrics). Original composer Hugh Martin made the changes, which included "Until then we'll have to muddle through somehow" becoming "Hang a shining star upon the highest bough."
The original lyrics for the film version were rejected by Garland and director Vincente Minnelli as too downbeat even for the situation in the film. Martin didn't want to change the lyrics and Garland threatened not to include the song in the film if the changes were not made. It was pointed out to Martin that it was to his extreme financial advantage that Garland sing this song in what was sure to be a hit film. Martin changed the lyrics, Garland sang the song, and the result was countless millions in royalties.
https://www.youtube.com/watch?v=MKG5X0QMSWA