What is the take home message from this thread? Well, in part it seems to be this:
According to the majority of Biblical scholars nowadays, only part of the present Book of Isaiah predates the departure of Lehi's party from the old world shortly before the fall of Jerusalem. Part, but not the whole, of their reasons for so thinking is that the second part of Isaiah refers by name, as if he was present, to Cyrus, who liberated the Jews from the captivity in Babylon that the first Isaiah had described as imminent but still in the future.
However the Book of Mormon quotes from this second part of Isaiah, which (so the argument goes) could not have been in the scriptures that Lehi's party took to the New World. In order to avoid this problem, it is necessary to accept that the whole of Isaiah predates the exile to Babylon, so that the whole of the present book of Isaiah could have been carried with them by Lehi's party. That implies a belief that the references to Cyrus as liberator were true prophecy, in the sense of true predictions of the future (names and all) made well before the event.
So accepting the Book of Mormon means accepting that such simple prediction does occur years before the event.
OK, if that is the way you want it ... but shouldn't that mean that the second part of Isaiah would get important things about Cyrus right, if it even gave us his name long before he was born? Isaiah chapter 45 tells us that he will liberate peoples exiled by the Babylonians after conquering their empire, which which is what Cyrus in fact did. Isn't it clear however from Isaiah chapter 47 that the writer is also predicting the destruction of Babylon at Cyrus's hands - which is exactly what the LDS scripture chapter heading says it is about;
Babylon and Chaldea will be destroyed for their iniquities—No one will save them.
But although the hope that Cyrus would be a liberator was fulfilled, Babylon surrendered peacefully and continued to be a prosperous city under his rule for years to come. A secular scholar sees this as a sign that the second part of Isaiah was written during the rise of Cyrus, when his policy towards exiled peoples was becoming clear, but before his conquest of Babylon, which (disappointingly for some Jews no doubt) he did not destroy. A believer in prophecy has to take the line that as a prophet Isaiah got one thing right:
1. A conqueror called Cyrus would overthrow the Babylonian empire, thus allowing the Jews to return home.
And got one thing wrong:
2. That conqueror would destroy Babylon.
No doubt Isaiah was only 'speaking as a man' when he got the destruction of Babylon wrong?