The title points to tarantism, the name given to a compulsive, frenzied dancing, and the poem treats that dancing as a response to fear. The opening two lines state it plainly: dancing out of fear is "a great disorder." The speaker sounds less like a celebrant than a diagnostician, noticing that what looks like release is really a kind of sickness.
The middle image shifts to water draining away with the tide, "green and cold as old meat." It's an unpleasant comparison, mixing the natural world with something dead and spoiled. The mood turns bleak here, as if whatever is leaving, whether calm, life, or comfort, leaves behind something rotten.
The last two lines move into "we," so the speaker is no longer standing apart. "We danced and broke / to be less like God" suggests people wore themselves out, maybe even damaged themselves, to escape being whole or all-powerful. The feeling is uneasy and a little grim, and the poem leaves the exact meaning open. It reads like a confession wrapped in a warning.