Brent A. Strawn describes the common interpretations of Isaiah authorship.
Brent A. Strawn, "The Prophets," The Old Testament: A Concise Introduction (New York: Routledge, 2019) 71-119
The Book of Isaiah has been called the Shakespeare of the Old Testament and the Fifth Gospel of Christianity. It is among the most beloved of prophetic books and is also among the most difficult since, according to current scholarly perspectives, it contains material that spans hundreds of years, from the time of the eighth-century prophet, Isaiah the son of Amoz, of Jerusalem, all the way through the Babylonian exile and well into the postexilic period. It has long been a scholarly standard to divide Isaiah into three unequal parts that reflect this range:
•Isaiah 1–39, called Proto- or First Isaiah;
•Isaiah 40–55, called Deutero- or Second Isaiah;
•Isaiah 56–66, called Trito- or Third Isaiah.
This division associates each of the major parts with a different time period and author(s):
•First Isaiah with the eighth-century prophet, Isaiah of Jerusalem, who was active from 738 until at least 701, maybe even as late as 688 bce;
•Second Isaiah with an anonymous prophet active during the later years of the Babylonian exile (ca. 545–539 bce); and
•Third Isaiah with an anonymous prophet (or prophets) who lived after the edict of Cyrus in 538 bce that allowed the Judean exiles to return home (see Chart 2.1).
Not surprisingly, many scholars have found this division too neat and tidy. According to many, not all of Isaiah 1–39 can be confidently traced back to the eighth century because this lengthy block of material is itself obviously composite. Isaiah 36–39 is a mostly prose narrative borrowed from the account in 2 Kgs 18:13–20:19 (see also 2 Chr 32:1–24). These chapters of Isaiah seem to function as a bridge from Isaiah 35 to Isaiah 40, where Second Isaiah begins. Scholars have also noted that the themes that are so pronounced in Second Isaiah—themes of comfort and hope—are also found in Isaiah 34–35, which presently stands in First Isaiah. Perhaps this is a sign that the author responsible for Second Isaiah edited First Isaiah.
As for Third Isaiah, most scholars think Isaiah 56–66 is not nearly as coherent as Second Isaiah. Does this mean that more than one anonymous prophet was responsible for Third Isaiah with the result being that the number of “Isaiahs” should be increased beyond three? Some interpreters believe that the core of Third Isaiah, chapters 60–62, bear notable similarity to Second Isaiah. Perhaps that is a sign that the “Third” (or higher number) Isaiah is responsible for the final editing of this lengthy book. Or does it mean that there are really only two “Isaiahs,” First and Second, with the latter extending from chapter 40 through chapter 66? Another vexed interpretive question is if these units—however many are identified—were originally discrete, existing independently of one another, or if Second Isaiah was from its inception conjoined with First Isaiah, or Third Isaiah with Second (and First) Isaiah.
Here, as in all instances of composition- and redaction-critical analysis, much remains uncertain and, finally, unknowable. What is clear, regardless, is that the Book of Isaiah, no less than other books in the Hebrew Bible—and in truth perhaps far more than most of them—is the end result of a long set of processes. It is also clear that the tone of the book shifts rather markedly in chapter 40. First Isaiah, or at least those parts of chapters 1–39 that scholars attribute to the eighth-century prophet, is marked by oracles that announce judgment on Jerusalem and Judah for wrongdoing, especially concerning matters of social injustice. First Isaiah also warns of the coming of Assyria, which God will use as a punitive tool against Judah (see, e.g., Isa 7:20; 10:5–15). In some ways, this thematic comes to its conclusion in chapter 39 where Isaiah promises King Hezekiah that destruction and exile are imminent (vv. 5–7). But then, unexpectedly, Isaiah 40 rings out:Comfort, O comfort my people! says your god.Speak tenderly to Jerusalem, and cry to herthat she has served her term, that her penalty is paid,that she has received from the Lord’s hand double for all her sins. (40:1–2; NRSV)
Most interpreters are agreed, not only on the basis of this verse, but of all else that follows in chapters 40–55, that the “penalty” that has been paid here refers to the destruction of Jerusalem, the fall of Judah, and the exile to Babylon. Second Isaiah is thus something of an extended poetic argument convincing the exiles that, despite judgment and punishment, God now intends to do a “new thing” (43:19). That new thing involves a return from exile that is comparable to a new exodus (see, e.g., 43:16–21; 51:9–11).
This shift is quite unexpected after the first 39 chapters. Equally unexpected is that one of the ways God will do this new thing is by using the Persian king, Cyrus, who is mentioned in 44:28 and 45:1, with the latter verse going so far as to call Cyrus the “anointed one” or Messiah of God! The specific mention of Cyrus by name is one of several reasons that scholars date Second Isaiah to the time of the Babylonian exile. Prophets, after all, were not primarily concerned with predicting far distant events (see above). Though the prophetic books frequently do discuss eschatological elements—texts that speak about the end (eschaton in Greek) of the world or of an epoch/era—they typically do not detail specific names of rulers hundreds of years before they are born. As one noted scholar put it, if chapters 40–55 were spoken by the eighth-century prophet Isaiah, seeking to address the needs of exiles who lived a century and a half after he lived, “it would be a situation without parallel in the rest of the Old Testament.”
Whatever the case, there is wide agreement that Second Isaiah contains some of the most beautiful poetry in the Hebrew Bible. Many scholars also believe that Second Isaiah comes closest to what we would today call abstract or theoretical monotheism: that there are no other gods besides the Lord (see, e.g., Isa 44:8; 45:5–6, 14, 18, 21–22; cf. 40:18–20; 44:9–20).
As already noted, Third Isaiah doesn’t have the same feel as Sec-ond Isaiah. In fact, there are hints here and there that this mate-rial comes from a later period than Second Isaiah—after the return home from exile and the rebuilding of the temple (see 66:1)—and that things haven’t turned out as well as Second Isaiah envisioned. In Third Isaiah, Judah seems highly fractious, and a general note of disappointment about the time period is sounded—something that is echoed in other postexilic prophets like Haggai and Zechariah (see below).
In the current form of the Book of Isaiah, all three “Isaiahs” are connected and attributed to Isaiah of Jerusalem (Isa 1:1). This shows, on the one hand, that the words of the prophets were thought to be lively and highly relevant for future times. It also shows, on the other hand, that for this very reason the (original) words of the prophets were regularly expanded upon and updated to demonstrate their significance for later generations. This could be seen as a kind of “accretion model”—not entirely unlike supplementary hypotheses for the Pentateuch (see Chapter 2)—but it shouldn’t be understood as indicating that the various accreted parts of Isaiah have little or nothing to do with one another. On the contrary, the Book of Isaiah, as it now stands, contains all of this material: it is a book-length testimony to the interrelationship between these var-ious, sometimes distinct parts—even if that relationship isn’t always clear now.
In some cases, however, the relationship of the parts seems quite clear. Scholars have identified a number of unifying themes that appear across all parts of Isaiah. These include the emphasis on God, who is frequently referred to as “the Holy One of Israel” (e.g., Isa 1:4; 29:19; 40:25; 60:9), and special interest in Jerusalem (Zion), which God has chosen and is thus treasured and special. Writing much later, in the second century bce, the author of Sirach (see Chart 1.1) captured some of the range and themes of the Book of Isaiah as we now have it in a brief, but memorable, way, attributing all of it to Isaiah, Amoz’s son, from Jerusalem: In Isaiah’s time, the sun moved backward, and he extended the king’s life. By his great spirit, he saw what was to come, and he comforted those who mourned in Zion. He revealed forever what would beand hidden things even before they happened. (Sir 48:23–25; CEB)