Those who mistake the unessential to be essential and the essential to be unessential, dwelling in wrong thoughts, never arrive at the essential.

A teaching about category error. The verse does not say what is essential and what is not — that is for the reader to discover. The Buddha names only the failure mode: confusing one for the other. The image suggests a long search undertaken with the wrong map. One walks earnestly toward what is not essential and arrives, eventually, at not having moved at all. The first work of practice, the verse suggests, is not effort. It is the calibration of what one is actually walking toward.