"Comfort ye, comfort ye my people, saith your God. Speak ye comfortably to Jerusalem, and cry unto her, that her warfare is accomplished, that her iniquity is pardoned: for she hath received of the LORD's hand double for all her sins" (Isaiah 40:1-2).
These two verses introduce the so-called book of "Deutero-Isaiah," which Biblical critics (who deny that prophecy can be fulfilled) claim was written by a second Isaiah simply because it contains prophetic claims which have come to pass. The Lord Jesus, however, quoted more than once from both "divisions" of Isaiah, attributing both of them to the same inspired author, and He surely knew more about their true authorship than do modern liberals!
Actually, however, the two divisions of Isaiah are quite distinctive in their respective vocabularies, simply because their respective themes are different. In fact, the chapter structure of the two divisions is quite remarkable, possibly even providential. The first book (chapters 1-39) contains the same number of chapters as the Old Testament has books. Book II (chapters 40-66) contains 27 chapters, the same as the number of books in the New Testament. The New Testament portion begins with John the Baptist (Isaiah 40:1-5), just as the New Testament itself does, and ends with the new heavens and the new earth (Isaiah 65 and 66; compare Revelation 21 and 22).
The central chapter in the New Testament part of Isaiah is Isaiah 53, which contains the clearest and fullest exposition of the substitutionary death of Christ for our sins to be found anywhere in the Bible. And the central verse of this chapter (which actually should begin at Isaiah 52:13) is: "But He was wounded for our transgressions, He was bruised for our iniquities: the chastisement of our peace was upon Him; and with His stripes we are healed" (Isaiah 53:5). HMM