What is the significance of "Lo El Amim Rabim"?
Radak: Rabim refers to nations far away, that you never heard their language.
Malbim: Do not say that you will need to say your Nevu'ah in Leshon Kasdim so that also Goyim will understand. You are not sent to them!
Why does it say "Im Lo Aleihem Shelachticha"?
Rashi: This is a Shevu'ah. If I sent you to them, I swear, if they will not hear you! The verse should be re-arranged.
Radak: "Im Lo" is a Shevu'ah, e.g. "Im Lo Batim Rabim l'Shamah", "Im Lo Ka'asher Dimisi Ken Hayasah" (Yeshayah 5:9, 14:24), like one who says 'this will not be, if it will not be.' It is as if he said 'in truth, if I sent you to them, they will hear you, even if they do not understand your language, and you do not understand theirs; they will request someone to explain your Nevu'ah to them.
Malbim: Even though I did not send you to [the Goyim], "Hemah Yishme'u Elecha" - when your Nevu'ah becomes known, they will hear and accept.
