The speaker describes listening to music as being swallowed whole and swimming inside it, like a creature in a huge belly of sound. The whole poem stays inside this one image: music as water. It ebbs and flows, tosses the speaker around, and feels like being drowned, yet the chords act like a lifebuoy that keeps them afloat. That mix of losing control and being held up is what makes the experience so thrilling.
The mood is awed, joyful and a little giddy. Even the danger of "drowning" is described as "a thrill and a delight." The quiet passage is pictured as a waterfall that falls only to rise higher, which suggests that softness in music can lift a listener rather than let them sink. The last lines reveal what the speaker has been listening to: Mozart's Requiem, with each drop of sound joining into one masterpiece. The poem ends on admiration, as if the whole ocean had been a single perfect piece of music all along.