*
sigh* I'm not throwing anything away. Let's zoom out to verses 4-10 (1-3 are just an introduction):
4 Then the word of the Lord came to me, saying:
5 “Before I formed you in the womb I knew you; Before you were born I sanctified you; I ordained you a prophet to the nations.”
6 Then said I: “Ah, Lord God! Behold, I cannot speak, for I am a youth.”
7 But the Lord said to me: “Do not say, ‘I am a youth,’ For you shall go to all to whom I send you, And whatever I command you, you shall speak.
8 Do not be afraid of their faces, For I am with you to deliver you,” says the Lord.
9 Then the Lord put forth His hand and touched my mouth, and the Lord said to me: “Behold, I have put My words in your mouth.
10 See, I have this day set you over the nations and over the kingdoms, To root out and to pull down, To destroy and to throw down, To build and to plant.”
"Before I formed you in the womb I knew you" is not a statement unto itself. It's part of God's way of communicating to Jeremiah that he (Jeremiah) is part of a bigger plan that God's been working on since before he was born. He's just using some flowery language to do it.
Jump down to verse 9 where he says, "Behold I have put my words in your mouth." Did God actually put something in Jeremiah's mouth like a parchment or a small cuneiform tablet? No? So why are you taking verse 5 so literally?
When you interpret phrases like this without their context, you
are, in a sense, tossing away the other text. Maybe you don't discard it entirely, but you ignore it temporarily to make a point.