Isaiah

At least three prophets were responsible for the book of the prophet Isaiah, and perhaps more. Chapters 1 through 39 are primarily the messages of I Isaiah, the statesman prophet, whose ministry began during the reign of Uzziah, about 740 B.C. The second portion of the book, chapters 40 through 55, contains the work of the great unknown prophet, referred to as II Isaiah or Deutero-Isaiah, who preached to the Jews during the latter part of the Exile. Chapters 55 through 66 were written after the Jews returned from Babylonia, and the author is known as III Isaiah or Trito-Isaiah. The messages of these three men mark the highest point of Hebrew prophecy.

Metaphysically, Isaiah is the higher self in us which discerns the reality, the real character, of spiritual humanity, and fearlessly proclaims it. It is our spiritual understanding.
(Source: Fillmore Study Bible, Metaphysical Bible Dictionary)