Isaiah is one of my favorite books in the Bible. I learned something about Isaiah a few years ago that I had never seen before. Isaiah is divided into 66 chapters. Just as the entire Bible is comprised of 66 individual books, written over the course of about 4000 years of time (and not one jot or tittle contradicts another jot or tittle, even though they might be separated by thousands of years. His word is completely consistent and absolutely true, and our God is amazing).
In the first 39 chapters of Isaiah, the Lord speaks of His judgments. The first 39 books of the Bible comprise the Old Testament, and teach us of His law and His judgment. In the next 27 chapters of Isaiah, from chapter 40 to the end of the book, the Lord speaks of His comfort. The last 27 books of the Bible comprise the New Testament, and teach us of His grace and His mercy.
Isaiah had no way of knowing how much would be added to Scripture after his death. But the Lord knew. The Lord set the canon of Scripture, His living and breathing Word, long before man did. It is comforting, is it not, that when these news reports come out, as they do from time to time, of finding the lost gospel of Thomas or some such nonsense, so that the world is in a dither with doubts over our Bible, that there was a reason God intended for it to be lost all this time, LOL (if it is even authentic at all, which I doubt). Those words are not Spirit-breathed, as are the Scriptures we hold in our hands.
Of course we did not need to know this about Isaiah in order to have confidence that the Scriptures we have, which the church has had for 2000 years unchanged, are the Words of God and not the words of man. Just as we do not need to know that the stars declare of their Maker night to night to have confidence that the universe was created for a purpose. But confirmation is sweet.