Even though his father’s work exists on durable metal plates, Moroni understands that the preservation and recovery of the text will require divine intervention. This passage identifies the spiritual qualifications necessary to bring the book to light. It cannot be done unless that person’s eye is “single to [God’s] glory.” Moroni has just contrasted the plates’ physical and spiritual value; he now underscores the value of the plates’ spiritual content and admonishes the future translator to concentrate on bringing that important message to light.
Reference: The reference is to the Sermon on the Mount. In Matthew 6:22, the verse reads: “The light of the body is the eye: if therefore thine eye be single, thy whole body shall be full of light.” (See commentary accompanying 3 Nephi 13:22–23.) The particular form of this verse, that the eye would be “single to his glory,” influences both the Joseph Smith Translation of the Sermon on the Mount (where the phase is “if thine eye be single to the glory of God”) and the Doctrine and Covenants 4:5: “an eye single to the glory of God.”