Verses 10–13 continue Mormon’s summary of the Nephite return to goodness and prosperity. His intent is not historical, but symbolic and structural (following the “out-of-time” intent of verse 6 above). “An exceedingly fair and delightsome people” is standard Nephite prophetic language, positioned here to show the effect of the Messiah’s visit. The concept of “fair/white and delightsome” has long been an image of righteousness. (See commentary accompanying 2 Nephi 5:21.) Mormon thus demonstrates both the people’s righteousness and the fulfillment of prophecy:
And then shall they rejoice; for they shall know that it is a blessing unto them from the hand of God; and their scales of darkness shall begin to fall from their eyes; and many generations shall not pass away among them, save they shall be a pure and a delightsome people.
And it shall come to pass that the Jews which are scattered also shall begin to believe in Christ; and they shall begin to gather in upon the face of the land; and as many as shall believe in Christ shall also become a delightsome people. (2 Ne. 30:6–7)
While Mormon may not be alluding to this particular prophecy, it is quite appropriate. The shift from the law of Moses to the gospel of the Messiah simply highlights the Messiah’s new covenant.