"The Evolution of God" is not a relaxing book to read. It is filled with archeology, biblical literature, history, and various types of scholarship. The intent of the author is to provide an understanding that the concept "God" has a history. It has evolved from animism through polytheism to monolatry and then, monotheism is a somewhat logical, albeit convoluted, history.
The transition from one level of understanding to another involves cross-fertilization, i.e., believing in more than one God until Gods merge into one, incorporating features of both. And, then, there is a back and forth movement, i.e., beliefs discarded on one hand are kept alive on another. This form of evolution is referred to as cultural evolution. It is not as neat as biological evolution, but the history indicates that constructs, e.g., God, do evolve through cultural changes.
The fact that the understanding of "God" evolves by virtue of social forces "on the ground" does not necessarily disprove that there is a transcendent being. Politics, international relations, and economics helped to determine which God to align with or, at least, accept in a spirit of tolerance. As long as there was "gain" by tolerating/accepting the foreign God, why not have some sort of acceptance?
It appears that the notion of God is more expansive when there is a non-zero sum situation at hand. If we feel that our lot is better through tolerance, then our God will be seen as universal. If not, we tend to see God as vengeful, resulting in the horrible events detailed throughout history. While we can hope that nations will see that there is a non-zero sum situation involved for us all, i.e., we survive and thrive when we allow others to do so also, when segments see it differently, they can use all sorts of "sacred books" to justify violence and destruction.
There is little of "Christianity" in the life of Jesus. The Jesus we know through the Gospels is a construct built by believers (40-80 years after Jesus). What seems to be true is that Christianity with many of the features popular to the world is a creation of Paul. And, like in previous eras, it was in his interest to further interethnic relationships in order to promote his franchises of Jesus-followers. The more magnanimous features of Christianity,e.g., loving your enemy, was a development designed to promote tolerance to the powerful in order to lessen their antagonism to this new religion. Expansion into the Roman Empire required more acceptance of other ethnic groups if the early Christians were to survive.
The development of Koran follows similar trends. When Muhammad was in Mecca where he initially was "inspired", his message to a polytheistic society was not received well. He was in no position to promote revenge directly. The Koran written under these circumstances encouraged more tolerance of those who were the oppressors. But, when he went to Medina and is message was supported by the majority, then the message was far more revengeful. The political and economic realities of the moment help determine the messages of Jesus and Muhammad.
Since the Books of the various religions (Judaism, Christianity, Islam) were written by people over time in circumstances that were perceived as either zero sum (producing intolerant, belligerent verbiage) or non-zero sum (producing more tolerant, compassionate texts), anyone can find something to support their views. The problem today is that the need to become tolerant in a clearly interdependent, non-zero sum world is sometimes jeopardized by the few who exercise extreme violence based on their perception of a zero sum situation.
The problem often times is that the hatred and violence of some result in a reaction that gives support to the belief systems of our enemies. Terrorists today are recruited because of the alignment of terrorists beliefs with their perceived reality, e.g., if Muslims claim justification for the behavior because the West hates them, won't our bombing and violence against our enemies who are Muslim, reinforced the basic premises of their behavior?
In order for the planet to survive, there is a need for people to use their moral imagination to reach beyond their more narrow perceptions in order to see how others are, in fact, interdependent with us. We have to work to make their "world" more aligned with ours in the sense that they see their "salvation" dependent on our behavior and vice versa.
Based on the title of the book, "The Evolution of God", one has to hope that "God" will clearly evolve to promote a higher degree of morality to enable humanity, now an interdependent global reality, to survive!
While the above captures the general thrust of the author's book, I clearly view the notions that God has "revealed" himself through written sources traditionally believed by the major religions as false. I can understand how someone could conclude that there may be a "higher power", but I cannot understand how humans could possibly have any comprehension of what this means. If there is a God, God remains clearly beyond our capacity to understand.