John Goldingay in The Theology of the Book of Isaiah doesn’t use the term “Second Isaiah”. But he argues that the next section or collage of Isaiah has material from more than a century after the oracles and narratives of chapters 1-39.
Chapters 40-55 leap over the period and kings following Hezekiah (around 700 BCE) and the decades following the two exiles (597 and 587) to address Jews who live in the time of the rise of Cyrus the Persian (the 540s). Goldingay cannot decide whether these addressees are in Babylon or Jerusalem. The chapters deal with both places and Jews in either place would have found the references to the two cities relevant.
A major theme of these chapters is that Yahweh alone is God.
A thing often said about these chapters is that they are the clearest Hebrew Bible statement of monotheism. Goldingay doubts that scribes and prophets in the Isaiah school thought in those terms. Monotheism is the belief that there is only one God. This is not the concern of this book.
“Its point is not that there is only one God as opposed to there being two or three of six or a hundred. It is that Yahweh alone is God. There are many other supernatural beings in existence, but they don’t deserve to be honored by the designation “God” even though we might call them gods with a small g (or one could think of them as spirits or demons or angels). Isaiah is not concerned with how many gods there are (the monotheism-polytheism question) as with the question of who is God.”
I agree with this. It is not a falling away from Christianity or Judaism to speak of gods. I have a friend who is a perfectly good Christian and fellow Kansas City Royals fan. Every day lately he has published on social media a prayer to the gods of baseball. (With tongue in cheek I suggested to him that the prophets might not have liked this and that Baal was a mispronunciation of Ball.) However, I do not really think the prophets would worry about this. The actual Baal was proposed as a rival of Yahweh. The gods of baseball are a joke, and perhaps a way of acknowledging the irrational elements that go into winning or losing (see Ecclesiastes 9:11).
But even thinking rightly or wrongly that there are real supernatural entities besides God is not to deviate from biblical faith. I tend to be skeptical and to treat them as jokes (this is my approach to Halloween when I wear a demon mask). But I could be wrong.
Some have proposed that Isaiah’s critique of idolatry is unfair to paganism or polytheism because sophisticated pagans do not actually think the physical idol is a god. Isaiah mocks idol worship as though the idol was the actual god. But pagans distinguished between the image as a representation or, perhaps, a manifestation of the god and the god itself.
Goldingay says Isaiah’s authors know this but find idolatry unworthy because Yahweh is the only God who stands sovereign over the whole cosmos and cannot be compared to entities who can be represented by images of created things.
“Should I bow down to a block of wood?” (Isaiah 44:19). If you can make a block of wood into something that represents a god it can’t be much of a god, certainly not comparable to Yahweh. In Isaiah 46:1-7 the point is that an idol has to be carried in a parade, but the real God is one who carries his people.
My view on this is that the ban on idol worship correlates to the name of God meaning something like “I will be what I will be.” To represent God by an image carries the danger of limiting God, putting God in a box. It is an attack on the freedom of God. It is a way of not letting God be God.
However, there is something to the Eastern Orthodox argument that the Incarnation has changed this. Now there is in Jesus a true image of God. Thus the use of icons in worship. Still I think the Jewish hesitation to represent God too precisely in words or images has value and I would rather err in that direction.