בְּטֶ֨רֶם אצורך [אֶצָּרְךָ֤] בַבֶּ֙טֶן֙ יְדַעְתִּ֔יךָ וּבְטֶ֛רֶם תֵּצֵ֥א מֵרֶ֖חֶם הִקְדַּשְׁתִּ֑יךָ נָבִ֥יא לַגּוֹיִ֖ם נְתַתִּֽיךָ׃
"Avant que je t’eusse formé dans le sein de ta mère, je te connaissais; avant que tu fusses sorti de ses entrailles, je t’avais consacré, je t’avais désigné comme prophète des nations."
Rashi on Jeremiah
When I had not yet formed you in the womb, etc. Since the days of the first man. The Holy One, blessed be He, showed Adam each generation and its prophets.
Rashi on Jeremiah
I...formed you Heb. אצרך, an expression of צורה, a form.
Rashi on Jeremiah
I knew you connois toi in O.F. Comp. (Exodus 6:3), “I was not known (נודעתּי) to them.”