This verse may be the most important in Malachi’s chapter. In Israel, the believers who still worshipped Yahweh had a “book of remembrance written.” It is the earthly counterpart of the heavenly book in which, according to Philippians 4:3, the names of the righteous are written: “And I intreat thee also, true yokefellow, help those women which laboured with me in the gospel, with Clement also, and with other my fellowlabourers, whose names are in the book of life.” Revelation 13:4–8 comments on this book in more detail:
And they worshipped the dragon which gave power unto the beast: and they worshipped the beast, saying, Who is like unto the beast? who is able to make war with him?
And there was given unto him a mouth speaking great things and blasphemies; and power was given unto him to continue forty and two months.
And he opened his mouth in blasphemy against God, to blaspheme his name, and his tabernacle, and them that dwell in heaven.
And it was given unto him to make war with the saints, and to overcome them: and power was given him over all kindreds, and tongues, and nations.
And all that dwell upon the earth shall worship him, whose names are not written in the book of life of the Lamb slain from the foundation of the world. (emphasis mine)
In Hebrew history, this book inscribes the names of the righteous in a permanent, heavenly record, assuring that Yahweh would remember them, even when the world did not. However, the Nephite context is very different. Jesus is teaching them the value of written scriptures, so the book of remembrance is the Book of Mormon itself. The Lord has told them that a landmark event preceding the Triumphant Messiah’s return will be the coming forth of their record. (See commentary accompanying 3 Nephi 21:2–3.) Their scriptures are so important that the Messiah himself examines them for accuracy and completeness. (See commentary accompanying 3 Nephi 23:8–11.) Thus, he quotes this scripture to punctuate his message about the importance of the scriptural record.