The speaker feels surrounded by water. The first lines suggest an overwhelming "abundance of sea," while the land itself seems to be turning liquid, so nothing solid is left to stand on. In response, the speaker does something oddly casual: rents a raft and eats tongue. It's a strange, almost comic image, and the poem doesn't explain it. Calling Chance a "chapel" turns luck into something like a sacred place, and the "fat joy" found there feels indulgent, even a little absurd, as if pleasure is being grabbed in the middle of a flood.
The ending shifts the tone. The speaker studies how the day "dissolved / without fire," which echoes the water imagery but adds loss, since nothing dramatic happened to end it. It simply slipped away. Being "sad in mind" is stated plainly. The mood is drifting and dreamlike, with flashes of dark humor, and a quiet sadness underneath. The speaker seems to cope with an uncertain, unstable world by surrendering to it, though the joy doesn't quite cancel out the sorrow.