RobH_en_tn/jer/49/31.md

Arise! Attack ... themselves

Here Yahweh is speaking to Nebuchadnezzar as if he was there listening to him. (See: rc://en/ta/man/translate/figs-apostrophe)

Attack the nation at ease, that lives in safety

Here "nation" represents the people living there. Alternate translation: "Attack this nation, whose people feel safe and secure" (See: rc://en/ta/man/translate/figs-metonymy)

They ... them

The words "They" and "them" refer to the people who feel safe and secure.