Nephi, the son of Helaman, spoke to the people in the city of Zarahemla concerning Jeremiah's prophecies of Jesus Christ:
And now I would that ye should know, that even since the days of Abraham there have been many prophets that have testified these things; yea, behold the prophet Zenos did testify boldly; for the which he was slain. And behold, also Zenock, and also Ezias, and also Isaiah, and Jeremiah, (Jeremiah being that same prophet who testified of the destruction of Jerusalem) and now we know that Jerusalem was destroyed according to the words of Jeremiah. O then why not the Son of God come, according to his prophecy? (Helaman 8:19-20)
According to John Tvedtnes, the declaration in Helaman 8:19-20 suggests that several ancient prophets, including Jeremiah, had prophesied of the coming of Christ. But there are no specific prophecies of Christ in the biblical book of Jeremiah. To be sure, Jeremiah 31:31-34 speaks of a new covenant to be established, but it does not mention Christ, who brought that new covenant. How, then, do we explain Nephi's statement to the people in the city of Zarahemla that Jeremiah had prophesied of Christ?
The book of Jeremiah is, after all, not an historical book, but a collection of prophecies with an interspersing of personal recollections by the prophet. The lack of chronological order of the various revelations suggests that the book of Jeremiah is a later collection of separate documents, to which a preface was added (Jeremiah 1:1-3). Because it was not written as a single book it is possible that some of Jeremiah's writings never made it into the collection.
The idea that Jeremiah wrote more than is in the biblical book that bears his name is supported by early Christian tradition as well as the Septuagint version of Jeremiah. We have, for example, the testimony of two second-century Church Fathers, Justin Martyr and Irenaeus. Writing of Christ's preaching to the dead while his body lay in the tomb, each of them attributed to Jeremiah a prophecy not found in the biblical account, in which the prophet wrote that the Lord would descend to preach salvation to the dead. Justin Martyr wrote:
And again, from the sayings of the same jeremiah these have been cut out [by the Jews]: "The Lord God remembered His dead people of Israel who lay in the graves; and He descended to preach to them His own salvation." (Dialogue with Trypho 72)
Irenaeus cites the same passage in Against Heresies 4:22.
The Book of the Bee, written in the Syriac language in the thirteenth century by the Nestorian bishop Solomon, has preserved an earlier tradition of another non-biblical prophecy of Jeremiah, declaring that,
This (prophet) during his life said to the Egyptians, "A child shall be born--that is the Messiah--of a virgin, and He shall be laid in a crib, and He will shake and cast down the idols" From that time and until Christ was born, the Egyptians used to set a virgin and a baby in a crib, and to worship him, because of what Jeremiah said to them that He should be born in a crib. (Book of the Bee 32)
The story is drawn from The Lives of the Prophets 2:8-10, a text that a number of scholars have suggested was originally written in Hebrew by Egyptian Jews during the lifetime of Jesus himself. It should be noted that after the Babylonians destroyed Jerusalem and its temple in 587 B.C., Jeremiah remained in Jerusalem under a Jewish governor named Gedaliah. When Gedaliah was assassinated, the Jews feared Babylonian reprisals and decided to flee to Egypt. They forced Jeremiah to go with them (Jeremiah 41-43). Some of Jeremiah's last prophecies were recorded in the Egyptian city of Tahpenhes (Jeremiah 43:8; 44:1)
Another Christian document known from medieval manuscripts in various languages is 4 Baruch, which is subtitled "The Things Omitted from Jeremiah the Prophet." The Ethiopic version attributes the book to Jeremiah's scribe Baruch, but the Greek says it was written by Jeremiah. Chapter 9 has Jeremiah prophesying of the coming of Jesus Christ, the Son of God, of his selection of twelve apostles, of his death and resurrection after three days, and of his return in glory to the Mount of Olives. According to the account, Jeremiah was stoned for this declaration. [John A. Tvedtnes, "Jeremiah's Prophecies of Jesus Christ," in The Most Correct Book, pp. 99-103, 58] [See the commentary on 1 Nephi 1:19-20]