I find it neat to see how chapters of Isaiah often tell us which audience is being addressed. I note this in the at least three of the first four chapters that are carried in the Book of Mormon.
Isaiah 48 (I Nephi 20) says, "Hear ye this, O house of Jacob, which are called by the name of Israel, and come forth out of the waters of Judah, which swear by the name of the Lord, and make mention of the God of Israel, but not in truth nor in righteousness."
Interestingly, in I Nephi 20, after saying the people he is speaking to are those who come out of the waters of Judah, it clarifies that that means out of the waters of baptism.
In the 1 Nephi 20 telling, it says they, "swear by the name of the Lord, and make mention of the God of Israel yet they swear not in truth or in righteousness. Nevertheless, they call themselves of the holy city, yet they do not stay themselves upon the God of Israel."
The Latter-day Saints call themselves of the holy city, and are out of the waters of baptism. But, I suppose it might also be referring to Christianity, in general, for Christians today have baptism and perhaps consider themselves to be of the holy city.
Chapter 49 also tells us who is being addressed. "Listen, O isles, unto me, and hearken, ye people from far." It seems this would be the people dispersed across the globe as Israel was scattered.
Chapter 51 might be speaking to those who are part of God's church, or who are at least seeking to do right in God's eyes. "Hearken to me, ye that follow after righteousness," it says. I do not know, but I wonder if it is speaking -- perhaps among others -- to the Latter-day Saints, for they follow after righteousness.
If you want to understand Isaiah, it seems important to take note of who is being spoken to. It becomes a key, helping us understand things that some say are hard to understand.
