Title Page vs 1 Nephi

A simple question:

The Title Page states that the Book of Mormon is an abridgment of the records of the Nephites and the Jaredites. The text explains it was abridged by Mormon and Moroni.

Then why does the book start with the very first verse, “I, Nephi?”

That's not an abridgement. That's an original first-person account.

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The answer is in D&C 9 and 10. See if anyone discusses this in Come Follow Me this year.

D&C 9 (directed to Oliver Cowdery)

I would that ye should continue until you have finished this record, which I have entrusted unto him.

2 And then, behold, other records have I, that I will give unto you power that you may assist to translate.

(Doctrine and Covenants 9:1–2)

What are the "other records" here?

When Joseph and Oliver finished translating the abridged plates that Joseph found in Moroni's stone box, including the Title Page which was on the "last leaf" of the set of plates, they considered starting over at the beginning to retranslate the Book of Lehi, which was the 116 pages that Martin Harris lost.

In D&C 10, the Lord told them not to do that. Instead, the Lord had other records for them to translate; i.e., the original plates of Nephi, which we refer to now as the "small plates of Nephi."

38 And now, verily I say unto you, that an account of those things that you have written, which have gone out of your hands, is engraven upon the plates of Nephi;

 39 Yea, and you remember it was said in those writings that a more particular account was given of these things upon the plates of Nephi.

40 And now, because the account which is engraven upon the plates of Nephi is more particular concerning the things which, in my wisdom, I would bring to the knowledge of the people in this account—

 41 Therefore, you shall translate the engravings which are on the plates of Nephi, down even till you come to the reign of king Benjamin, or until you come to that which you have translated, which you have retained;

42 And behold, you shall publish it as the record of Nephi; and thus I will confound those who have altered my words.

(Doctrine and Covenants 10:38–42)

The key point here is that Joseph did not have the plates of Nephi when he was in Harmony. These plates were obviously not in the collection of plates Joseph found in the stone box. 

Before leaving Harmony, Joseph gave the plates to a divine messenger he later explained was one of the Three Nephites. After David Whitmer picked up Joseph and Oliver to take them to his father's home in Fayette, they encountered the messenger on the road. David offered him a ride but the messenger declined, explaining that he was "going to Cumorah." This chance encounter was apparently a way to inform Joseph that the repository of Nephite records was in Cumorah as explained in Mormon 6:6. 

Naturally, the messenger returned the abridged plates to the repository, picked up the small plates of Nephi, and took those plates to Fayette for Joseph to translate.

And that's why our modern Book of Mormon starts with "I, Nephi" instead of the abridged records that Mormon compiled.

(click to enlarge)