en_tn/jer/10/08.md

They are both brutish and stupid

The words "brutish" and "stupid" mean basically the same thing and emphasize how foolish the people are for worshiping idols. Alternate translation: "They are all very stupid" (See: rc://en/ta/man/jit/figs-doublet)

Their vain discipline—it is nothing but wood

The writer writes as if he gets halfway through his statement and cannot continue. "As for what they work so hard to serve, it is only a piece of wood"