A prophet of the Lord is one who speaks on behalf of the Lord, or in his name, whether he predicts future events, or unfolds the past, or gives commandments and rules for present conduct. To hear the words of the prophet is to consider them carefully and to do readily whatever the Lord, through his prophet, requests or commands.
The Lord said to his people concerning the Law, when all was prepared:
"For this commandment which I command thee this day, it is not hidden from thee, neither is it far off. It is not in heaven, that thou shouldst say, Who shall go up for us to heaven, and bring it unto us, that we may hear it and do it? Neither is it beyond the sea, that thou shouldst say, Who shall go over the sea for us, and bring it unto us, that we may hear it and do it? But the word is very nigh thee, in thy mouth, and in thy heart, that thou mayest do it." (Deut. 30:11-14)
Which is as much as to say that the Lord does not require anything strange and exceptional of his people. What he demands is that they do that which they know in their hearts to be true, and which perhaps they confess and proclaim with their lips as the word of the Lord.
The explanation of this chapter and the next, as given by Nephi in his discourse to his fellow travelers, is found in Chapter 22.