Before I formed thee, &c.— See Isaiah 49:1-5. We have examples of a similar designation with that mentioned in the text, in St. John the Baptist, and St. Paul.
Related Commentaries of Jeremiah 1:5
Jeremiah 1:5
5 Before I formed thee in the belly I knew thee; and before thou camest forth out of the womb I sanctified thee, and I ordaineda thee a prophet unto the nations.