God already had Jeremiah in mind before he was born. At that time, he was already occupied with Jeremiah. Jeremiah 1:5 uses different verbs to indicate this: formed, knew, consecrated, and appointed (as prophet). Before his birth, God had set him apart for a special task: to be God’s prophet to all nations.
5 “Before I formed you in the womb I knew you, and before you were born I consecrated you; I appointed you a prophet to the nations.”