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

In plain words: Here the verse is compared to the sky and the song to the air, because the air rests in the sky. That is why the song is sung resting on the verse.