When Nephi paraphrased Isaiah 29 in the 2 Nephi 27, he appropriated Isaiah's words to the coming forth of the Book of Mormon. He adapted them making a paraphrase rather than a quote. (I explain the reasons for this in Nephi's Isaiah.) Here he uses the Isaiah materials again to identify who he (Nephi) is: "the voice of one crying from the dust." The primary audience for his writings will be those who come to read the book in the last days; when mankind will be in possession of the record which has been printed and distributed to the masses.
Nephi's primary audience for his teachings are those who, like us, live in the last days after the Book of Mormon has come to light. Although Nephi's descendants would have access to these same records, their greatest work and worth would be in the last days. Hence Nephi identifying himself as a "voice of one crying from the dust."
There is also a secondary meaning. Because Nephi was mortal, he was made of the "dust of the ground." (Moses 3: 7.) He was a man testifying to the truthfulness, as a witness in mortality, of the great things which exist beyond the veil. He is one of us, and yet able to tell us of things to come. Therefore, his witness is given in mortal weakness, but with the power of God behind it. His own strength is dust. The power of Christ to redeem, however, is without limit.
Three distinct groups are addressed in the message: Nephi's descendants, called his "beloved brethren." They are "brethren" rather than "children" because they would descend primarily from his brother's seed who would overcome his. But there would be a mixture of his among them. So they were his "brethren."
The second are called "those who are of the house of Israel." These are the Jews, or others who keep their identity with Israel. Not the gentiles, who have been lost and must gain covenant status one by one, and thereafter live true to the covenant in order to be redeemed. "Those who are of the house of Israel" have been previously identified and discussed by Nephi in the Nephi 28.
The final group is "all ye ends of the earth." That is, the gentiles, heathen, and those who are not otherwise included even in prophetic mention. All mankind. All the ends of the earth may receive what is offered and attain to covenant status, if they repent, acting no deception, without hypocrisy, following Christ. And all are included in the broad sweep of Nephi's invitation to come to Christ.
His "farewell" is "until that great day shall come." That day is when you see the Lord in judgment with Nephi there beside Him. At that time you will be "face to face" with Nephi, accounting for your heed or neglect of his message. He just mentioned that in the prior verses. He now bids you good-by until that moment. So you should look forward to meeting Nephi at this point. Although you need to take his message seriously if you intend to enjoy the moment.
What other prophets have warned us that their message will confront us in the presence of Christ while he, the prophet-messenger, is there with us at the moment of judgment? Nephi is in a very small group of qualified messengers whose words should be taken with soberness and respect. He is a towering figure when measured by the correct standard. We seldom encounter such a man. When we do, we would be well advised to take counsel from him.
What more can he have said to alert us to the importance of his message?