Answer
The book of Isaiah was written by the prophet Isaiah. The book is categorized as one of the Major Prophets in the Old Testament or, in the Hebrew Tanakh, as a Latter Prophet. The term major refers to the length of the books rather than the credentials or importance of the authors. In the Tanakh, prophets like Isaiah, Jeremiah, and Ezekiel are termed “Latter Prophets” to distinguish them from the Former Prophets such as Samuel and Nathan.
Isaiah prophesied during the time of the divided kingdom under the reigns of Uzziah, Jotham, Ahaz, and Hezekiah, kings of Judah. Isaiah likely prophesied between 739—681 BC, a time when both the northern and southern kingdoms had turned away from God. Israel fell to Assyria in 722 BC, and Judah continued its trajectory of rebellion against God. Tragically, the warnings of Isaiah and other prophets changed nothing, and Judah later fell to the hands of Babylon. Isaiah also contains many Messianic prophecies, including Isaiah 7:14; 9:6–7; and 11:1–5. The prophet probably died during the reign of Manasseh. Tradition states that Isaiah was martyred.
The book of Isaiah opens with a line that identifies the author: “The vision concerning Judah and Jerusalem that Isaiah son of Amoz saw during the reigns of Uzziah, Jotham, Ahaz and Hezekiah, kings of Judah” (1:1). As with other books of both the Major and Minor Prophets, the book of Isaiah was named after the author.
Some modern scholars challenge the traditional authorship of Isaiah, proposing a multi-authorship view. They divide the book into three sections (chapters 1—39, 40—55, and 56—66) supposedly written by different authors at different times. The three supposed authors are given the names Proto-Isaiah, Deutero-Isaiah, and Trito-Isaiah (First, Second, and Third Isaiah). There is no basis for such claims except for some stylistic differences and the fact that the writer sometimes speaks of future events as if they had already occurred. An instance of the past tense used to describe future events is called “prophetic perfect tense”; a good example is Isaiah 53, where the suffering of the Messiah is spoken of as if it had already happened. Bible commentator Charles Swindoll explains the artificial division of Isaiah as arising from “a scholarly denial of predictive prophecy. This position not only limits the power of God to communicate with His people but also ignores the wide variety of specific, predictive claims about Jesus Christ scattered throughout the book” (https://insight.org/resources/bible/the-major-prophets/isaiah, accessed 2/6/24).
Arguing against the claim of multiple authorship is the fact that the book of Isaiah has always existed as a single collection. Further, it has always been called “Isaiah.” The oldest extant copy of Isaiah, found among the Dead Sea Scrolls, is dated from c. 175 BC. That copy of Isaiah is a single scroll. From beginning to end, it is undivided, and the transition between chapters 39 and 40 (one of the major divisions, according to the “three Isaiahs” theory) is seamless. Nothing in any ancient copy of Isaiah even hints that the scribes thought the book should be divided into different sections or that they were dealing with different authors.
In summary, Isaiah is the author of the book bearing his name. Proposals of multiple authorship should be rejected. The book, one of the most beautifully written in all of Scripture, remains relevant for Christians due to its wide-ranging prophecies, its warning about the dangers of sin and the certainty of judgment, and its presentation of God’s mercy and restoration.
