Rik is the stars, Sâman the moon. This Sâman (moon) rests on that Rik (stars). Therefore the Sâman is sung as resting on the Rik. Sâ is the stars, ama the moon, and that makes Sâma.

In plain words: The verse is compared to the stars and the song to the moon, which moves among the stars. So the song rests on the verse.