Why was the text of the Book of Mormon changed from "white and delightsome" to "pure and deliighsome"?

In the 1840 edition of the Book of Mormon Joseph Smith changed, “a white and delightsome people” to “a pure and delightsome people.” The original reading of “white and delightsome” was retained in LDS textual tradition which followed the 1841 edition is Great Britain rather than the 1840. The 1981 edition of the Book of Mormon restored Joseph Smith’s 1840 reading of “pure.” The change was likely made by Joseph Smith to emphasize the spiritual rather than biological nature of the blessing prophesied by Nephi.