en_tn/jer/15/19.md

you will be like my mouth

Jeremiah is compared to the mouth of Yahweh because he will be used to speak Yahweh's message. AT: "you will speak for me" (See: rc://en/ta/man/translate/figs-simile)

you yourself

The pronoun, "yourself", is used here to emphasis the command was specifically for Jeremiah. (See: rc://en/ta/man/translate/figs-rpronouns)