Although there is no MS—even the oldest, among the Dead Sea scrolls—which in any way suggests that the book can be divided among several authors of different dates, it has been modern critical opinion that the book cannot have been wholly composed at the same time. Some conservative scholars who maintain the unity of the Book's authorship by Isaiah, son of Amoz in Jerusalem, do so on the ground that unity is presupposed by the NT in Matt. 3: 3, 12: 17 f. and Rom. 10: 20 f. So, it is held, chs. 40–66 consist of a core of prophecies of Isaiah of Jerusalem, though contemporary allusions have been incorporated by later editors.

The case for the critical position is that the historical situation envisaged in Isa. 1–39 is for the most part that of the second half of the 8th cent. BCE whereas in Isa. 40–66 (and also Isa. 13–14) the references to Cyrus and the end of the Exile in Babylon clearly derive from the 6th–5th centuries. This analysis is confirmed by the difference of themes: the ‘First Isaiah’, the prophet who lived in court circles in Jerusalem during the 8th cent., interprets the Assyrian threat to Judah in the light of his belief about God’s providence. The unknown prophet of the exilic period, who is never named (though it has been suggested that he was also called Isaiah) saw the collapse of Babylon and the triumph of the Persian Cyrus in 539 BCE (Isa. 44: 28; 45: 1). So a prominent theme is that of the restoration of the Temple. It is also shown by computer analysis that the Hebrew of 40–66 has many subtle variations from 1–39.

However, the diverse historical contexts cannot disguise an underlying theological unity of the whole book, which is impressive enough to suggest very competent editorial redaction. Yahweh is designated ‘the Holy One of Israel’ in both parts of the book (1: 4; 10: 20; 41: 14), illustrating this theological and literary unity. The nation’s failures are punished; and the hope (40–55) of ultimate restoration implies conditions (56–66) of no further lapses into the former apostasies (1: 21)—though, to be sure, in so much that it is written in poetic form there cannot be any discernible historical sequence. Maybe a school of Isaianic expositors were responsible for collating such miscellaneous material as was available; it included the apocalyptic section (24–27) and a straight historical section (36–39) (which largely reproduces 2 Kgs. 18–20).

A modern reader cannot ignore the expertise of historical criticism. And at the same time he or she may also find it hard not to relate to the prophetic warnings (e.g. Isa. 5: 8) to events in Palestine of the 21st century.

Isa. 1–39 contains the prophet’s denunciations of the sins of Judah and Jerusalem (1–12) and invectives against the leaders (22: 15–25). There are oracles against foreign nations (13–23), and prophecies of hope, denunciation, and salvation (24–35). Finally, 36–9 is a prose appendix, possibly not written by Isaiah, giving an account of his relations with King Hezekiah, and parallel to 2 Kgs. 18: 13–20: 19. Some of Isaiah’s ethical judgements are governed by OT codes (e.g. Exod. 23) while others seem to derive from the universal moral sense of what is right and wrong, as in the Wisdom literature (e.g. Proverbs).

First Isaiah is concerned with two major political crises: the Syro-Ephraimite conspiracy (734–733 BCE) when Judah’s two northern neighbours in unison tried to force Judah into an alliance against Assyria. The second crisis was that of the Assyrian threat to Jerusalem of 701 BCE. In chs. 1–9 Isaiah tried to persuade King Ahaz that the two conspirators were doomed to fail. God’s promise to David (2 Sam. 7) was unbreakable (Isa. 9: 1–6; 11: 1–10). However, Ahaz decided to seek Assyrian help (2 Kgs. 16: 7 f.) against the two allies, and Isaiah prophesied that this act of faithlessness, and the social evils of the country, would deserve God’s punishment by war.

Syria and Ephraim were conquered, and the Assyrians made Judah a vassal state. Assyrian cult objects were introduced by Ahaz into the Temple (cf. 2 Kgs. 16: 11). However, Hezekiah, who succeeded Ahaz in 715 BCE, threw off the yoke of Assyria, with some encouragement from Egypt (Isa. 18: 1–2 and 30: 1–7), and at the same time purged the country of foreign idolatry in a reform which anticipated that of Josiah (629 BCE). Inevitably Sennacherib, king of Assyria, marched against Judah, but Hezekiah paid tribute and escaped his wrath (701 BCE).

The situation for Second Isaiah was the Exile of the people of Judah in Babylon (2 Kgs. 24: 12–16). It was a captivity in which the people enjoyed liberty of worship; synagogues may have been established then, and observance of the sabbath was emphasized. Business prospered. Nevertheless many remembered their homeland with affection (Ps. 137). So the prophet celebrates Cyrus emperor of Persia as God’s agent for reversing the exiles’ fortunes. In 538 BCE Cyrus issued a proclamation allowing the return to Jerusalem, but the prophecies of 2 Isaiah had probably been delivered about 547 BCE when Cyrus was beginning his career of conquest. 2 Isaiah’s message is that Yahweh is the only God and he will bring salvation to his people. In chs. 56–66 the style and tone is more critical of the nation, and some scholars regard this section as the work of a third prophet, designated ‘Trito-Isaiah’.

An important section of Deutero-Isaiah is that of the four Servant Songs: 42: 1–4; 49: 1–6; 50: 4–11, and 52: 13–53: 12. Much scholarly discussion has been devoted to the identity of the servant. Was he an individual—e.g. Jeremiah? Or a group? Or the nation as a whole? Or the ideal nation? Because these sections became important for Christian propaganda as seemingly referring to Jesus (Matt. 12: 16–21; 1 Pet. 1: 24–5) they have sometimes been isolated from the rest of the book, although the ‘servant’ is mentioned in 41: 8; 45: 4, outside the Songs. At any rate their meaning is that it is through failure and humiliation that God’s promise is revealed and fulfilled. In addition to the Servant Songs, the book contains the Emmanuel prophecy (7) and the house of David motif (9 and 22), which made Isaiah, together with the Psalms, the most quoted OT books in the NT.