God touches Jeremiah’s mouth and says he has put his words in Jeremiah’s mouth (Jeremiah 1:9). The act directly links Jeremiah’s message to God’s own words.
In Jeremiah 1:8–10, Yahweh answers Jeremiah’s fear about facing hostile people. He tells Jeremiah not to be afraid because Yahweh will be with him and rescue him. Yahweh then acts out the promise by touching Jeremiah’s mouth and declaring that Yahweh’s own words are now placed in Jeremiah. These verses belong to Jeremiah’s call narrative at the opening of the book (Jeremiah 1:4–19). Jeremiah has already been told that his role will bring resistance, and he has voiced his hesitation about speaking.
These verses present God’s answer to Jeremiah’s fear about facing real opposition (“them”). The main reassurance is not Jeremiah’s courage but God’s presence: “I am with you,” with the stated purpose of delivering him (explicit claim).
A careful answer keeps the immediate passage, the book's argument, and the whole-Bible storyline together, so the question is answered in context instead of as a detached idea.
Start with Jeremiah 1:9, then read the surrounding section so the answer stays connected to the passage's flow.
9Then Yahweh put forth his hand, and touched my mouth; and Yahweh said to me, Behold, I have put my words in your mouth: