This is the charge given by Christ to the twelve whom He had called and given power to baptize. It was overheard by those who had been witnessing these events. But the charge is to the twelve.
The obligation to declare the doctrine of Christ, preach repentance, baptize with authority and make known the Father, Son and Holy Ghost is imposed upon the twelve. This burden, therefore, rests on them and is theirs to bear off "unto this people." They are to warn everybody of these obligations. Not just those who were there.
The extent of the duty runs "unto the ends of the earth." From where they were at the time Christ was preaching, to the entire North and South American continents and all those who may be living there at the time were the assigned mission field to whom the doctrine of Christ was to be declared.
The break between this portion of Christ's teachings and what would follow is interesting to consider. The remainder of His teachings will form the primary message foundational to Christianity. It is the new, higher law which replaces the earlier Law of Moses. Yet this portion, declared by Christ as His "doctrine" is the part to be taken first and declared everywhere. Why?
A fair conclusion to reach is that before you consider the new, higher law you must first:
These things precede His replacement of the older, lower law with His new, higher law. It is reasonable to conclude you will not comprehend His follow-on teachings if you have not first repented, been baptized, received the Holy Ghost, and understand the Godhead. Or, even more to the point: You will never be able to LIVE His new, higher law unless these steps are taken first. Until then you may aspire, but you will not be able to live them. They address the heart, rather than just conduct. They go to the deepest convictions inside you, what motivates you, and the reasons for your conduct. Your conduct will follow these precepts when you have been changed. For the required change, the tools discussed first must be acquired.
He will return to the themes of this opening statement, declaring nothing more or less than what He has taught should be given as His. (See 3 Nephi 18: 12-13.)
So we turn from this introductory, first statement of His doctrine to His great foundational Sermon at Bountiful in which the higher law is first given in one, complete statement of what we are to become. It is not merely direction to us. It is also a revelation of what kind of person Christ was. He explains it Himself...