The Gospel will be preached as a witness to all nations, and everyone in the entire world will hear the Gospel at least once, no matter where they are, or how remote their home may be. It's not certain if this will be fulfilled before the rapture, or after during the Tribulation. However, evidence suggests this is most likely to happen just before the rapture.
(*Do you have a better description, or did you find an error? Please let me know.