Katherine Mansfield's short story "Her First Ball" explores a number of themes, including the heightened sensitivity of youth, gender roles, and the fleeting, temporary nature of time.
A key thematic line demonstrating the heightened sensitivity of youth is,
Leila was sure if her partner didn't come and she had to listen to that marvellous music and to watch the others sliding, gliding over the golden floor, she would die at least, or faint.
This quotation alludes to the exaggerated sensitivity and self-consciousness of youth. Leila, the protagonist of the story, is desperately anxious that she will be left alone and, worse, be seen to be alone, which of course would be horribly embarrassing.
One key thematic line for the theme of gender roles is,
Why didn't the men begin? What were they waiting for?
Here, the narrator channels the thoughts of Lelia. She, like the other women present, expects the men to make the first move. They, the ladies, are expected to be passive, while the men are expected to be active.
The fat man who talks to Leila at one point tells her that one day she will be old, like him, and that when she is old she will see things quite differently than how she sees them now. He says to her,
your pretty arms will have turned into little short fat ones, and you'll beat time with such a different kind of fan—a black bony one . . . And you'll smile away like the poor old dears up there, and point to your daughter, and tell the elderly lady next to you how some dreadful man tried to kiss her at the club ball. And your heart will ache, ache.
This is of course a rather mean-spirited thing to tell to a young woman enjoying her first ball, but, nonetheless, it also has some truth to it, and it's all the more depressing for that. Leila's beauty will, as the fat man suggests, fade over time, as will her innocence, and as might her enthusiasm for life.