20 And moreover, I say unto you, that the time shall come when the knowledge of a Savior shall spread throughout every nation, kindred, tongue, and people. ...23 And now I have spoken the words which the Lord God hath commanded me.24 And thus saith the Lord: They shall stand as a bright testimony against this people, at the judgment day;
I have never noticed the use of the word "bright" to describe the words he is speaking. It connects very clearly to the words of Alma-2 to his son Helaman as he passed along the records:
4 Behold, it has been prophesied by our fathers, that they should be kept and handed down from one generation to another, and be kept and preserved by the hand of the Lord until they should go forth unto every nation, kindred, tongue, and people, that they shall know of the mysteries contained thereon.
5 And now behold, if they are kept they must retain their brightness; yea, and they will retain their brightness; yea, and also shall all the plates which do contain that which is holy writ.
Update: Mormon says something very similar in Words of Mormon verse 11.