The voice of the Lord comes to Nephi. The first declaration is a typical, yet important, beginning. Nephi is told that he has done well. That is important, for it would be easy for Nephi to feel that he had been a failure. He had had remarkable success among the Lamanites, only to be ineffective in the north, and now unable to change his own people (who Mormon implies are affected by the north, or the north-connected Gadiantons).
Thus, the blessing would come as a comfort for a Nephi who could easily have become discouraged.
Next comes the important statement: “Thou are Nephi, and I am God.” This sounds like so much truism that we could miss that the impact of the statement is an echo of Leviticus 26:12: “I will walk among you, and will be your God, and ye shall be my people.” Jehovah is reiterating that covenant with Nephi, in a very real, and very personal, sense.
The next reason for the declaration that it is Jehovah who is speaking is to declare that He has the power to control the earth. Jehovah can “smite the earth with famine, and with pestilence, and destruction, according to the wickedness of this people.” More importantly, Jehovah grants that power to Nephi: “Ye shall have power over this people.” Nephi is given the power to do the miracles that Jehovah himself would.