1 Nephi 10:22

22 And the Holy Ghost giveth authority that I should speak these things, and deny them not.

When Nephi tells us that he is speaking with the authority of the Holy Ghost, he is telling us that his words are scripture. D&C 68:2–4 says that when those who are ordained to the priesthood, and their mission is to preach, speak when moved upon by the Holy Ghost (i.e. with his authority), it is scripture. These are the words, mind, and will of the Lord, and we should heed them.

• D&C 68:2–4