Mafalda's poem starts with rain, but it is really about feeling unwanted. In the first two stanzas, she points out a strange habit: people call rain beautiful and say they can't wait for it, yet the moment it arrives they run for cover. The praise is easy. Actually standing in it is not.
In the last stanza, the speaker turns the comparison on herself. She feels like rain. People tell her she's "a catch," which sounds like a compliment, but nobody follows it up by actually choosing her. They hide from her the way they hide from a shower.
The mood is quietly sad, with a hint of frustration. The language is simple and the rhymes are plain, which makes the hurt feel honest rather than dramatic. The speaker isn't angry, just puzzled and lonely, left with admiration that never turns into closeness. The wordplay on "catch" and "catch me" is the sharpest moment, since it shows how empty kind words can be.