1 Ne 9:2 they are called the plates of Nephi
Here Nephi describes the difference between the small plates and large plates. The large plates contained a full account of my people. The small plates contained the ministry of my people (verse 3). The small plates were large enough to contain 1 Nephi, 2 Nephi, Jacob, Enos, Jarom, and Omni. Nephi did not begin writing on these plates until 30 years after leaving Jerusalem (2 Ne 5:28-30).
1 Ne 9:5 the Lord hath commanded me to make these plates for a wise purpose in him
The foreknowledge of God had anticipated the blunder of the 116 lost pages of the book of Lehi. It was for this reason that the Lord commanded Nephi to write an abridged version of the same history on the small plates. He was to include the more plain and precious parts (1 Ne 19:3). This spiritual record would be translated instead of retranslating the book of Lehi contained on the large plates. Thus, the Lord would show that his wisdom is greater than the cunning of the devil. DC 10: 38-43 contains the Lord's commands to Joseph Smith to translate the small plates of Nephi to replace the history lost in the 116 pages:
'And now, verily I say unto you, that an account of those things that you have written, which have gone out of your hands (the 116 pages), is engraven upon the (small) plates of Nephi;
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.
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--
Therefore, you shall translate the engravings which are on the (small) 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; (i.e. those portions of Mosiah that had been translated but were not given to Martin Harris)
And behold, you shall publish it as the record of Nephi; and thus I will confound those who have altered my words.
I will not suffer that they shall destroy my work; yea, I will show unto them that my wisdom is greater than the cunning of the devil.
Behold, they have only got a part, or an abridgment of the account of Nephi.
Behold, there are many things engraven upon the plates of Nephi which do throw greater views upon my gospel; therefore, it is wisdom in me that you should translate this first part of the engravings of Nephi, and send forth in this work.' (DC 10: 38-43)
The ability of the Lord to foresee and make preparations for an event 2400 years in the future is remarkable. This wise purpose of the Lord was referred to in the following Book of Mormon scriptures, 1 Nephi 9:3,5, 1 Nephi 19:3, Words of Mormon 1:7.
Ezra Taft Benson
"The ancient preparation of the Book of Mormon, its preservation, and its publication verify Nephi's words that 'the Lord knoweth all things from the beginning; wherefore, he prepareth a way to accomplish all his works among the children of men; for behold, he hath all power unto the fulfilling of all his words' (1 Nephi 9:6). We are not required to prove that the Book of Mormon is true or is an authentic record through external evidences-though there are many. It never has been the case, nor is it so now, that the studies of the learned will prove the Book of Mormon true or false. The origin, preparation, translation, and verification of the truth of the Book of Mormon have all been retained in the hands of the Lord, and the Lord makes no mistakes. You can be assured of that." (The Teachings of Ezra Taft Benson, p. 65.)
1 Ne 9:5 a wise purpose...which...I know not
Nephi knew why he had to leave Jerusalem. He knew why he had to return to get the brass plates. He knew why he had to kill Laban, and he knew why he had to return for the family of Ishmael. But why he had to make a duplicate record of his history and a record of his ministry, he did not know. Yet, Nephi is content to follow the commands of the Lord without knowing all His plans. His faith is not blind; his obedience is not blind because he knows that the Lord has a "wise purpose" for the record. How different is that from the carnal man, who will never follow an order unless he understands why? Nephi never seems upset by the Lord's apparent silence on the matter. He never demands a reason. He just faithfully keeps the command of the Lord at considerable personal sacrifice. Imagine how much work it must have been for him to record everything written in 1st and 2nd Nephi! Then imagine how much we would have lost had he not been faithful or was not content in the knowledge that 'the Lord knoweth all things' (v. 6).