When God called Jeremiah to serve him and to be a prophet to the nations, Jeremiah tried to worm out of this task by claiming that he was too young and inexperienced. God saw through his tactic and told Jeremiah to stop using that as an excuse.
In essence, I see this as God reminding Jeremiah, that when we fulfil God's calling, we are given God's resources to complete the task. This is what God said (Jeremiah 1:4-8):
“Before I shaped you in the womb,I knew all about you.
Before you saw the light of day,
I had holy plans for you:
A prophet to the nations—
that’s what I had in mind for you.”
6 But I said, “Hold it, Master God! Look at me.
I don’t know anything. I’m only a boy!”
7-8 God told me, “Don’t say, ‘I’m only a boy.’
I’ll tell you where to go and you’ll go there.
I’ll tell you what to say and you’ll say it.
Don’t be afraid of a soul.
I’ll be right there, looking after you.”
God’s Decree.