2 Nephi 1:27

"And it must needs be that the power of God must be with him, even unto his commanding you that ye must obey. But behold, it was not he, but it was the Spirit of the Lord which was in him, which opened his mouth to utterance that he could not shut it."

Lehi is teaching his sons Laman and Lemuel that Nephi was not commanding them because he felt like it. Rather, Nephi was a prophet of God filled with His Spirit. Nephi talked with the power of God. His words were the words of the Lord. Laman and Lemuel did not understand that their brother was speaking on behalf of deity, just as all true prophets do.