A film is - or should be - more like music than like fiction. It should be a progression of moods and feelings. The theme, what's behind the emotion, the meaning, all that comes later.
If Wagner lived today, he would probably work with film instead of music. He already knew back then that the Great Art Form would include a sort of fourth dimension; it was really film he was talking about.
To make the listener listen, the theme is repeated stressing a variant: it is a principle of music to repeat the theme. Repeat and repeat again, as the pace mounts.
This short article from The Script Lab makes a great point about music and writing.