Jeremiah objects to his commission by saying he does not know how to speak because he is "only a youth" (Jeremiah 1:6). The statement explains his hesitation as inexperience and fear about speaking publicly.
In Jeremiah 1:4–7 the story of Jeremiah’s call begins with Yahweh speaking to him. Yahweh says Jeremiah’s role was not an accident of the moment: before his birth, Yahweh already “knew” him, set him apart, and appointed him as a prophet with a message that reaches beyond Judah. These verses sit at the front of the book as part of Jeremiah’s call narrative, explaining why he speaks with authority and why his words must be heard.
Jeremiah’s authority is presented as starting with God’s initiative: “the word of Yahweh” comes to him (verse 4). The call is framed as intentional and prior to Jeremiah’s own awareness: God says he “knew” Jeremiah before forming him, “set him apart” before birth, and “appointed” him as a prophet (verse 5).
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 1:6, then read the surrounding section so the answer stays connected to the passage's flow.
6Then said I, Ah, Lord Yahweh! behold, I don`t know how to speak; for I am a child.