3 Nephi 5:12-14

Mormon continues:

¹² And behold, I am called Mormon, being called after the land of Mormon, the land in which Alma did establish the church among the people, yea, the first church which was established among them after their transgression. 

¹³ Behold, I am a disciple of Jesus Christ, the Son of God.  I have been called of him to declare his word among his people, that they might have everlasting life. ¹⁴ And it hath become expedient that I, according to the will of God, that the prayers of those who have gone hence, who were the holy ones, should be fulfilled according to their faith, should make a record of these things which have been done—

3 Nephi 5:12 - 14

Apparently, for the first time in his record, Mormon introduces himself to us.  He would alter write in the Words of Mormon discussing the plates,

And they were handed down from king Benjamin, from generation to generation until they have fallen into my hands.  And I, Mormon, pray to God that they may be preserved from this time henceforth.  And I know that they will be preserved; for there are great things written upon them, out of which my people and their brethren shall be judged at the great and last day, according to the word of God which is written.

Words of Mormon 1:11

He was named after the land of Mormon where Alma₁ established the first church after their transgression.

We know this was an important land to him.  Commenting on Alma₁’s work there, he wrote:

And now it came to pass that all this was done in Mormon,

yea, by the waters of Mormon,

   in the forest that was near the waters of Mormon;

   yea, the place of Mormon,

      the waters of Mormon,

      the forest of Mormon,

   how beautiful are they

      to the eyes of them

      who there came

         to the knowledge of their Redeemer;

   yea, and how blessed are they,

   for they shall sing to his praise forever.

Mosiah 18:30

We learn he is a disciple of Christ.  He was called by Christ to declare the gospel to his people.  And now I, Mormon, speak unto you, my beloved brethren; and it is by the grace of God the Father, and our Lord Jesus Christ, and his holy will, because of the gift of his calling unto me, that I am permitted to speak unto you at this time” (Moroni 7:2).

He is keeping the records so that the prayers of those in the past would be fulfilled.  The record would be kept and preserved for those who will come.

And now behold, this was the desire which I desired of him—that if it should so be, that my people, the Nephites, should fall into transgression, and by any means be destroyed, and the Lamanites should not be destroyed, that the Lord God would preserve a record of my people, the Nephites; even if it so be by the power of his holy arm, that it might be brought forth at some future day unto the Lamanites, that, perhaps, they might be brought unto salvation—

For at the present our strugglings were vain in restoring them to the true faith.  And they swore in their wrath that, if it were possible, they would destroy our records and us, and also all the traditions of our fathers.

Wherefore, I knowing that the Lord God was able to preserve our records, I cried unto him continually, for he had said unto me: Whatsoever thing ye shall ask in faith, believing that ye shall receive in the name of Christ, ye shall receive it.

And I had faith, and I did cry unto God that he would preserve the records; and he covenanted with me that he would bring them forth unto the Lamanites in his own due time.

And I, Enos, knew it would be according to the covenant which he had made; wherefore my soul did rest.

And the Lord said unto me: Thy fathers have also required of me this thing; and it shall be done unto them according to their faith; for their faith was like unto thine.

Enos 1:13 - 18

The Lord also said:

And this testimony shall come to the knowledge of the Lamanites, and the Lemuelites, and the Ishmaelites, who dwindled in unbelief because of the iniquity of their fathers, whom the Lord has suffered to destroy their brethren the Nephites, because of their iniquities and their abominations.

And for this very purpose are these plates reserved, which contain these records—that the promises of the Lord might be fulfilled, which he made to his people;

D&C 3:18 - 19

And, behold, all the remainder of this work does contain all those parts of my gospel which my holy prophets, yea, and also my disciples, desired in their prayers should come forth unto this people.

And I said unto them, that it should be granted unto them according to their faith in their prayers;

Yea, and this was their faith—that my gospel, which I gave unto them that they might preach in their days, might come unto their brethren the Lamanites, and also all that had become Lamanites because of their dissensions.

Now, this is not all—their faith in their prayers was that this gospel should be made known also, if it were possible that other nations should possess this land;

And thus they did leave a blessing upon this land in their prayers, that whosoever should believe in this gospel in this land might have eternal life;

D&C 10:46 - 50