en_tn/1ki/14/23.md

For they also built

The word "they" here refers to the people of Judah.

built for themselves

The words "for themselves" are a metonym for what they will do with the high places. Alternate translation: "built for their own use" (See: rc://en/ta/man/jit/figs-metonymy and rc://en/ta/man/jit/figs-rpronouns)

on every high hill and under every green tree

This is likely to be an exaggeration that indicates there were many places like these for false worship all over the country. Alternate translation: "on the high hills and under the green trees" (See: rc://en/ta/man/jit/figs-hyperbole)