These verses are a transition from the command to write. The context is the Book of Mormon’s coming forth to fulfill the Savior’s prophecy. Here, however, he does not stress its appearance as a harbinger of end-time, but as part of the law against which humankind will be judged. Human beings who possess the scriptures will be judged by how well they obey the commandments contained in them. Although the context is specifically the Book of Mormon, it included the brass plates for the Nephites and, for us, the Bible, Doctrine and Covenants, and Pearl of Great Price.
Although Jesus says, “all things are written by the Father,” he was speaking metaphorically. The Father is the source of the revelations that become the scriptures, so they metaphorically are his “writings.” We can be validly judged out of the books because they contain the will and words of the Father.
Reference: Similar language is found in Revelation 20:12: “And I saw the dead, small and great, stand before God; and the books were opened: and another book was opened, which is the book of life: and the dead were judged out of those things which were written in the books, according to their works.”
The book of life in Revelation, however, is never physical. It symbolizes God’s knowledge of our actions and our hearts. In 3 Nephi, scriptures are literal writings. Thus, this “book” fits the context of the Savior’s discourse to the Twelve (3 Ne. 16:4) and to the multitude (3 Ne. 23:4).