Isaiah (; Greek: Ἠσαΐας, Ēsaiās ; Arabic: اشعیاء, Ash-ee-yaa ; "Salvation of/is YHWH") is the main figure in the Biblical Book of Isaiah, and is traditionally considered to be its author. He was an 8th-century BC Judean prophet who declared that all the world belonged to God and that God will destroy it. "The earth will be completely laid waste and totally plundered. The LORD has spoken this word." (Isaiah 24:3). Isaiah therefore warns the people of the world to turn back to God.
He prophesied during the reigns of Uzziah (or Azariah), Jotham, Ahaz, and Hezekiah (1:1), the kings of Judah. Uzziah reigned fifty-two years in the middle of the 8th century BC, and Isaiah must have begun his career a few years before Uzziah's death, probably in the 740s BC. He lived till the fourteenth year of Hezekiah (who died 698 BC), and may have been contemporary for some years with Manasseh. Thus Isaiah may have prophesied for the long period of at least forty-four years.
In early youth Isaiah must have been moved by the invasion of Israel by the Assyrian monarch Tiglath-Pileser III (); and again, twenty years later, when he had already entered on his office, by the invasion of Tiglath-Pileser and his career of conquest. Ahaz, king of Judah, at this crisis refused to co-operate with the kings of Israel and Syria in opposition to the Assyrians, and was on that account attacked and defeated by Rezin of Damascus and Pekah of Israel (). Ahaz, thus humbled, sided with Assyria, and sought the aid of Tiglath-Pileser against Israel and Syria. The consequence was that Rezin and Pekah were conquered and many of the people carried captive to Assyria ().
Soon after this Shalmaneser V determined wholly to subdue the kingdom of Israel, Samaria was taken and destroyed (722 BC). So long as Ahaz reigned, the kingdom of Judah was unmolested by the Assyrian power; but on his accession to the throne, Hezekiah, who was encouraged to rebel "against the king of Assyria" entered into an alliance with the king of Egypt (). This led the king of Assyria to threaten the king of Judah, and at length to invade the land. Sennacherib (701 BC) led a powerful army into Judah. Hezekiah was reduced to despair, and submitted to the Assyrians (). But after a brief interval war broke out again, and again Sennacherib led an army into Judah, one detachment of which threatened Jerusalem (). Isaiah on that occasion encouraged Hezekiah to resist the Assyrians whereupon Sennacherib sent a threatening letter to Hezekiah, which he "spread before the lord" ().
21 Then Isaiah son of Amoz sent a message to Hezekiah: This is what the lord, the god of Israel, says: Because you have prayed to me concerning Sennacherib king of Assyria,
22 this is the word the lord has spoken against him: The Virgin Daughter of Zion despises and mocks you. The Daughter of Jerusalem tosses her head as you flee.
23 Who is it you have insulted and blasphemed? Against whom have you raised your voice and lifted your eyes in pride? Against the Holy One of Israel!
According to the account in Kings (and its derivative account in Chronicles) the judgment of God now fell on the Assyrian army. "Like Xerxes in Greece, Sennacherib never recovered from the shock of the disaster in Judah. He made no more expeditions against either southern Palestine or Egypt."
The remaining years of Hezekiah's reign were peaceful (). Isaiah probably lived to its close, and possibly into the reign of Manasseh, but the time and manner of his death are not specified in either the Bible or recorded history. There is a tradition that he suffered martyrdom in the pagan reaction in the time of Manasseh. Both Jewish and Christian traditions state that he was killed by being sawed in half. Some interpreters believe that this is what is referred to in the New Testament verse, which states that some prophets were "sawn in two". It is also mentioned in the book of The Martyrdom of Isaiah that he lived into the days of Manasseh, and was also sawn in half with a wooden saw.
In the 1700s, the break between the first part of Isaiah (Is. 1-39) versus the latter half of the book (Is. 40-66) caught the eye of critical scholars Döderlein (1789) and Eichhorn (1783), who advocated a source-critical reading of the book, seeing chapters 40-66 as later, post-exilic additions, or even totally separate works artificially appended to the earlier composition. The term "Deutero-Isaiah" described the anonymous later writer, to whom some ascribed some redactionary roles as well. Some more recent commentators have further divided 40-66 by adding a third Isaiah, Trito-Isaiah, who wrote 56-66. The provenance of the text in the latter half of the book seemed to support a post-exilic timeframe, with direct references to Cyrus, King of Persia (, 13), a lament for the ruined temple, and other details. Also, the tone of the two halves is different; the first seems to warn erring Judah of impending divine judgment through foreign conquest, while the second seems to provide comfort to a broken people.
Other scholars, such as Margalioth (1964) challenged the view of multiple authorship by pointing out the remarkable unity of the book Isaiah in terms of theme, message, and vocabulary. Even certain verbal formulas unique to Isaiah, such as "the mouth of the Lord has spoken," appears in both halves of Isaiah but in no other Hebrew prophetic literature. While clear differences between the two halves of the book were evident, thematically the two halves are remarkably similar, certainly more similar to each other than to any other existing prophetic literature.
Since the late 20th century, trends in critical scholarship have focused on synchronic approaches, which advocate a whole-text reading, rather than the traditional historical-critical diachronic approaches, which tend to be directed at taking the text apart, looking for sources, redactional seams, etc. Inspired by Hebrew Bible literary criticism done by Robert Alter, scholars have since tended to circumscribe authorship and historical-critical questions and look at the final form of the book as a literary whole, a product of the post-exilic era which is characterized by literary and thematic unity.