The book that Nephi beheld in vision and which "proceedeth out of the mouth of a Jew" and contained "a record of the Jews" (1 Nephi 13:23) is evidently our present Old Testament. Reynolds and Sjodahl indicate in the following statement the appropriateness of these terms in referring to the Old Testament.
The prophet is here speaking of the Old Testament, as it was to appear through the labors of Ezra and his associates and successors.When Lehi left Jerusalem, the so-called canon of the Old Testament, as we know it, was not yet completed. The five books of Moses, undoubtedly, had been collected and written on one roll, numerous copies of which must have been in existence. The writings of the prophets, such as Joshua, the Judges, Samuel, Kings down to the reign of Zedekiah, and the prophecies of Isaiah, Hosea, Amos, Micah, and parts of Jeremiah, and their contemporaries, Joel, Amos and Jonah, must have existed in separate volumes, and individual collectors may have owned more or less complete sets. The Book of Job, some of the Psalms, the Proverbs, the Song of Solomon, and Ecclesiastes were also known, even if not generally accepted as sacred scripture. There were also books by authors whose names are mentioned in the Bible, but whose writings have not come down to us. The collection of Laban, known in the Book of Mormon as the Brass Plates, must have been unusually complete, judging from the contents. It must have been a very valuable library. Such libraries must have been owned by prominent individuals.
Ezra undertook the work of collecting all the sacred writings that existed at his time. This work included not only the discovery of copies in various places, the rejection of those that were not authentic and the copying of manuscripts the contents of which could not otherwise be secured, but also the correction of the text, after careful examination of the variations that must have been found. It was this work that was shown to Nephi in his vision of the Old Testament, and therefore, he, very properly, says he beheld it coming "out of the mouth of a Jew."
This expression appears still more significant when we recall the fact that Ezra, after the completion of the Pentateuch, gathered the people and read it to them and expounded it for seven days, and submitted it to them for their acceptance (Nehemiah 8:1-18; 9:3). Then it, literally, proceeded out of the mouth of a Jew. This took place about 445 B.C., about 150 years after the exodus of Lehi.
The canon was gradually completed by the addition of the writings of Ezra, Nehemiah, and the prophets who lived during and after the exile, Ezekiel, Daniel, Obadiah, Habakkuk, Zephaniah, Haggai, Zechariah, and Malachi. The canon as thus completed was accepted by our Lord Himself, and it is, in this remarkable vision, called, on that account, "The Book of the Lamb of God" (1 Nephi 13:38). (Commentary on the Book of Mormon, 4:262-63.)