The speaker is an onlooker, set apart from the busy world. People go about their business every day of the week, and the speaker watches them "slide," a word that makes their movements look smooth, automatic, almost effortless. Life becomes a kind of dance, and everyone seems to know the steps.
The middle stanza turns to questions. What "jig" demands that we keep the world running? And what is it about a "contented life" that irks? The questions are hard to pin down. They might be aimed at the crowd's relentless routine, or at the speaker's own irritation, possibly even envy, at seeing others settled in it.
The last stanza leaves the speaker sitting with a "book of dances," studying the steps instead of joining in. "Serving time" suggests a sentence, as if this watching were a kind of confinement. The mood is quiet, wry, and a little lonely, caught between curiosity and resentment.