Hi Cold Steel,
"Note these two quotes, one from Isaiah and one from Micah. Did one quote the other, or did they both quote another source we don’t have?"
Here is the text of Isaiah 2 vs Micah 4. In both cases we know from ancient manuscripts this text is legitimately old.
Micah 4:1 But in the last days it shall come to pass, that the mountain of the house of the LORD shall be established in the top of the mountains, and it shall be exalted above the hills; and people shall flow unto it.
Isaiah 2:2 And it shall come to pass in the last days, that the mountain of the LORD's house shall be established in the top of the mountains, and shall be exalted above the hills; and all nations shall flow unto it.
Differences: (a) last days/come to pass vs come to pass/last days, (b) house of the LORD vs LORD's house.
Micah 4:2 And many nations shall come, and say, Come, and let us go up to the mountain of the LORD, and to the house of the God of Jacob; and he will teach us of his ways, and we will walk in his paths: for the law shall go forth of Zion, and the word of the LORD from Jerusalem.
Isaiah 2:3 And many people shall go and say, Come ye, and let us go up to the mountain of the LORD, to the house of the God of Jacob; and he will teach us of his ways, and we will walk in his paths: for out of Zion shall go forth the law, and the word of the LORD from Jerusalem.
Differences: (a) nations vs people, (b) go vs come, (c) ye, (d) law shall go forth/Zion vs Zion/go forth the law.
Micah 4:3 And he shall judge among many people, and rebuke strong nations afar off; and they shall beat their swords into plowshares, and their spears into pruninghooks: nation shall not lift up a sword against nation, neither shall they learn war any more.
Isaiah 2:4 And he shall judge among the nations, and shall rebuke many people: and they shall beat their swords into plowshares, and their spears into pruninghooks: nation shall not lift up sword against nation, neither shall they learn war any more.
Differences: (a) many people vs the nations, (b) afar off.
So what does this tell us? These verses are not exact word-for-word. Nonetheless there are long phrases of material that indicate a common source, Micah quoting Isaiah or visa versa. Since both are known to be from the same time period it (732 BCE for Isaiah, 716 BCE for Micah, as per New World Translation, Table of Bible Books). The Bible is a collection of books, wherein actual original sources are not known. Looking at the Bible as a single book is just not correct. Thus it is entirely reasonable to believe religious thoughts of the Jews were written in several places then finally collected and redacted to become the Bible books we have today. You'll notice for example Psalms 14 is repeated as Psalms 53. While a modern Bible makes it look like Psalms is one book, in reality it is a collection of psalms that were originally on different five different scrolls. Thus it should not be surprising that an one psalm wound up in two collections.
Notice too the type of difference here, one is word order and different words. This is what one would expect, for material from a similar source, but varied slightly, then translated into English. It is for these reasons why one cannot really deny KJV text is copied into the Book of Mormon.
Cheers,
-Randy