Now Mormon is coming to the end of the administration of Nephi III and so Mormon addresses his last two chapters to the Gentiles.
Mormon knew that the coming forth of the Book of Mormon would come at a time when the Gentiles had taken over nearly the entire continent of America. Therefore Mormon issues a warning to the Gentiles that when the Book of Mormon comes forth there are going to be some major changes.
The most significant thing about these two verses is the fact that conditions will begin to shift radically so that the descendants of Lehi will replace the Gentiles as the principal occupants of America. The cleansing of America and restoration of the American continent to its rightful heirs will take sufficient time to make some of the people think the Lord had delayed his coming.
Mormon warns the Gentiles and the Israelites who think the prophecies of the Lord have been postponed. The next three verses is the Savior's warning to both the Gentiles and Israelites.