Robert L. Cate's introduction to Isaiah in Mercer Dictionary of the Bible.
Robert L. Cate, "Isaiah, Book of," Mercer Dictionary of the Bible, ed. Watson E. Mills (United States: Mercer University Press, 1990), 414
Furthermore, those who support a non-Isaianic authorship of these chapters point to differences in style and theology. Numerous words and phrases found in one section are not found in the other. "The Lord, Yahweh of Hosts," "remnant," and "to stretch out the hand," are all quite common in chaps. 1-39, but do not appear in 40-66. Further, "in that day" occurs more than thirty times in chaps. 1-39 and once in 40-66. On the other hand, "all flesh," "to choose," "chosen," and "I, Yahweh [or some other name for God]" do not occur in chaps. 1-39, while appearing with frequency in 40-66. "Redeem" is found more than twenty times in chaps. 40-66 but only once in 1-39. Among the theological differences that have been noted is the fact that in chaps. 1-39 God's majesty is emphasized, the messiah is king, and Yahweh is related to Israel through a covenant commitment. In contrast, in chaps. 40-66 God's infinity is stressed, the messiah is suffering servant, and Israel is related to Yahweh through his redemptive choice.