1 Nep 6

 1 And now I, Nephi, do not give the genealogy of my fathers in^athis part of my record; neither at any time shall I give it after upon these ^bplates which I am ^cwriting; for it is given in the record which has been kept by my ^dfather; wherefore, I do not write it in this work.

 2 For it sufficeth me to say that we are descendants of ^aJoseph.

 3 And it mattereth not to me that I am particular to give a full account of all the things of my father, for they cannot be written upon ^athese plates, for I desire the room that I may write of the things of God.

 4 For the fulness of mine intent is that I may ^apersuade men to^bcome unto the God of Abraham, and the God of Isaac, and the God of Jacob, and be saved.

 5 Wherefore, the things which are ^apleasing unto the world I do not write, but the things which are pleasing unto God and unto those who are not of the world.

 6 Wherefore, I shall give commandment unto my seed, that they shall not occupy these plates with things which are not of worth unto the children of men.(I love that Nephi clarified all of this, because I know that everything in the Book of Mormon has a purpose of being there!  It is our job to figure out why it is there and why it is important that we know it!)