Question: "What is the Deutero-Isaiah theory? Was the Book of Isaiah written by multiple Isaiahs?"
Answer: Most Bible scholars are in agreement that Isaiah was the sole author of the book that bears his name. However, there are those “liberal” scholars who are skeptical about anything that points to supernatural inspiration of the Bible. In fact, they go so far as to explain the fulfilled prophecies in these books by re-dating them to after the events occurred! The theory of multiple Isaiahs is just another example of skepticism from those who want to call into question the Bible as God’s inspired Word.
This theory of “Deutero-Isaiah” (or second Isaiah) came about near the end of the eighteenth century. Supposedly, Isaiah himself wrote only the first 39 chapters, leaving one of his students to write the second part (chapters 40—66). This was done allegedly sometime after the Babylonian captivity started (after 586 BC). As such, this later date would explain explicit predictions of “Cyrus, King of Persia” in Isaiah 44:28—45:1.
The “Deutero-Isaiah” theory claims Isaiah chapters 40—55 contain no personal details of the prophet Isaiah as compared to Isaiah 1—39. The first section tells of numerous stories of Isaiah, especially his dealings with kings and others in Jerusalem. The theory goes on to say that the style and language of Isaiah 40—55 seem to be quite different from the earlier chapters. What is so interesting about this argument is that it is also promulgated by the authors who support one author for the book! One contention is that specific references to Cyrus began with the experiences of the exiles in Babylon. This last argument is supposedly the strongest. It claims the second part of the second part of Isaiah was written later because only a later date can explain the accuracy of the prophecy.
Again, most reputable Bible scholars reject the “Deutero-Isaiah” theory. Their conclusions include the similarity of writing styles in both sections, the consistent use of the same words throughout, and the familiarity of the author with Palestine, but not Babylon. Furthermore, Jewish tradition uniformly ascribes the entire book to Isaiah.
The Dead Sea Scrolls contain a complete scroll of Isaiah dated from the second century BC. The book is one unit with the end of chapter 39 and the beginning of chapter 40 in one continuous column of text. This demonstrates that the scribes who copied this scroll never doubted the singular unity of the book. Neither did the New Testament authors, nor the early church, as quotations from both sections are attributed only to Isaiah.
The book of Isaiah contains extensive and precise prophecies about the coming of the Messiah as well as the life and crucifixion of Christ. Briefly these include:
• The reign of Christ in the kingdom (Isaiah 2:3–5)
• The virgin birth of Christ (Isaiah 7:14)
• The reign of Christ (Isaiah 9:2, 7)
• Jesus’ rule over the world (Isaiah 9:4)
• Christ as a descendant of David (Isaiah 11:1, 10)
• Christ to be filled with the Spirit (Isaiah 11:2; 42:1)
• Christ to judge with righteousness (Isaiah 11:3–5; 42:1, 4)
• Christ to rule over the nations (Isaiah 11:10)
• Christ to be gentle to the weak (Isaiah 42:3)
• Christ to make possible the New Covenant (Isaiah 42:6; 49:8)
• Christ to be a light to the Gentiles and to be worshiped by them (Isaiah 42:6; 49:6–7; 52:15)
• Christ to be rejected by Israel (Isaiah 49:7; 53:1–3)
• Christ to be obedient to God and subject to suffering (Isaiah 50:6; 53:7–8)
• Christ to be exalted (Isaiah 52:13; 53:12)
• Christ to restore Israel and judge the wicked (61:1-3).
Messianic prophecy is strong and important evidence for Jesus’ claims to be God. Isaiah’s writings were completed many centuries before Jesus Christ was born and yet are completely accurate. Remember, the Dead Sea Scrolls contained more than one complete scroll of this book composed well before the birth of Christ. And the book of Isaiah was included in the Septuagint (LXX), the earliest version of the Old Testament Scriptures, translated at least 300 years earlier.
But by far the strongest evidence that proves the unity of the book of Isaiah is that Jesus Himself quoted from both the beginning and the end of the book, attributing all of it to Isaiah.
1. Jesus quoting from Isaiah 29:13: “Isaiah was right when he prophesied about you hypocrites; as it is written: ‘These people honor me with their lips, but their hearts are far from me. They worship me in vain; their teachings are but rules taught by men’” (Mark 7:6–7).
2. Jesus also referenced Isaiah 42:1–4 in Matthew 12:17: “This was to fulfill what was spoken through the prophet Isaiah.”
3. Isaiah is also referenced in Matthew 8:16–17 by quoting Isaiah 53:4: “This was to fulfill what was spoken through the prophet Isaiah: ‘He took up our infirmities and carried our diseases.’”
Aside from the passages quoted by Jesus above, several other New Testament verses refer to the prophet Isaiah as been the sole author: Matthew 3:3 and Luke 3:4 (Isaiah 40:3); Romans 10:16, 20 (Isaiah 53:1; 65:1); John 12:38-41 (Isaiah 53:1; 6:10). But the fact that our Lord Jesus affirmed Isaiah’s authorship by quoting from both sections of the book and attributing them to Isaiah is proof enough of the entire book’s authorship. Those who reject the words of the Lord Himself will never be convinced by any other means.