GaTech Raley wrote:
The ultimate purpose of his books are to encourage people to seek Christ, regardless what you think of the church.
First, there are degrees of apostasy. Israel was in a state of apostasy. They did not have the higher priesthood and many truths, they DID HAVE authority to administer the ordinances of the temple. Christ never disputed this. He acknowledged the Priestly authority of the time, even though they lacked the fullness.
POWER in the priesthood is DIFFERENT than AUTHORITY in the priesthood, the COJCOLDS teaches that they are synonymous, they are not. One may have authority but not power, "thus many are called, but few are chosen....." Lacking power is a state of apostasy.
Even though Israel lacked the fullness and were in a state of apostasy, there were some who still were able to commune and talk with God (Isaiah, Samuel, Daniel, etc.). Even thought the LDS church is in a state of apostasy, they do not have the fullness, they still have the authority to administer the ordinances. But this collective apostasy is no impediment to us being able to receive Christ now.
What is striking is the shared pride between Israel and the LDS church for being "chosen", yet they were both fallen. And you wondered why there are so many Isaiah chapters in the BoM.
So basically the purpose of this book is to tell people that belong to a religion based entirely on a mythical person that they have apostatized from the foundation of their core religion, of which there are several offshoots that fall closer to the original foundation than the mainstream, which was based on an unsubstantiated claim that two mythical beings visited a 14 year-old boy to tell him that all of the other religions based on one of the mythical beings were corrupt because 1000 years before there were several councils convened where-which scholars evaluated texts written second and third hand accounts of said mythical being to determine which accounts to canonize and which accounts to discard, along with how to incorporate existing pagan beliefs into this newly formed religion in order to make it more appealing to general masses and thus help it spread faster and easier, never mind the fact that there are absolutely no first-hand accounts of anything the aforementioned mythical did in its supposed mortal life, if there even was one ... that yet another person has now spoken to the mythical being in question and this mythical being has stated, surprise of all surprises, that the first religion is just as wrong as all the other religions that have come before it? Huh. Didn't see that one coming.

My, oh my, how history loves to repeat itself.
As for wondering why there are so many Isaiah chapters in the BoM, the answer to that is simple. It's called plagiarism. There's not an original idea to be found the BoM. Joseph Smith and Oliver Cowdery tried, but they failed miserably.
Sorry, GTR, but it's the same song and dance we've all heard before: All talk and no proof.