This is certainly not a recreational read ... much time is spent in the details of various primitive totemic religions (largely Aborigine), but also some reference to the religions of the native americans.
The basic truth painstakingly worked out is that we are "Moral Believing Animals". In short, humans are inherently social, they will form groups, and those groups will believe in something that is at its base not rational/proveable, but totally real and sacred to the group.
A religion is a unified system of beliefs and practices relative to sacred things, that is to say, things set apart and forbidden—beliefs and practices which unite into one single moral community called a Church, all those who adhere to them. The second element which thus finds a place in our definition is no less essential than the first; for by showing that the idea of religion is inseparable from that of the Church, it makes it clear that religion should be an eminently collective thing.
Scientism, historicism, materialism, Christianity, atheism, Taoism, Communism, etc are equal relative to being unverifiable in a philosophical sense. Since we can't philosophically/scientifically prove our existence, or even that we are "conscious" (which we also can't define), it is faith all the way down for all of us.
At the roots of all our judgments there are a certain number of essential ideas which dominate all our intellectual life; they are what philosophers since Aristotle have called the categories of the understanding: ideas of time, space,  class, number, cause, substance, personality, etc. They correspond to the most universal properties of things. They are like the solid frame which encloses all thought;
One of the best descriptions of our state is expressed in the deeply intellectual film "This is Spinal Tap" relative to the Druids:
In ancient times, hundreds of years before the dawn of history, lived an ancient race of people. The Druids. No one knows who they were or what they were doing.
Amazingly, I've been to Stonehenge, and that quote is etched in stone in the visitors center.
One of the base philosophical questions is "Why is there anything"? As the book says:
Thus we find that we have here two sorts of knowledge, which are like the two opposite poles of the intelligence. Under these conditions forcing reason back upon experience causes it to disappear, for it is equivalent to reducing the universality and necessity which characterize it to pure appearance, to an illusion which may be useful practically, but which corresponds to nothing in reality; consequently it is denying all objective reality to the logical life, whose regulation and organization is the function of the categories. Classical empiricism results in irrationalism; perhaps it would even be fitting to designate it by this latter name.
As we believe we have recently observed, "reality" is an illusion. It is all interacting fields.
We thus believe we discover that all our models ... the Platonic, the Aristotelian, the Newtonian, Einstein's static model, the Quantum model, the Standard Model, are all just that, "models". Models, like maps are very useful, however we need to always remember that the map is not the territory.
Durkheim is attempting to go back to the origin of religion, and one of the bases is what a group considers sacred vs profane. One of the laments we hear today is "is nothing sacred?". To classical empiricism, that there is no concept of sacred, and as stated above, classical empiricism as a way to understand the universe is irrational ... meaning "insane". An often heard question today is "has the world gone insane?". I'm pretty sure that Durkheim would say that is so, and a lot of evidence seems to support that view.
To distinguish religion from all other classification systems:
... it is absolute. In all the history of human thought there exists no other example of two categories of things so profoundly differentiated or so radically opposed to one another. The traditional opposition of good and bad is nothing beside this; for the good and the bad are only two opposed species of the same class, namely morals, just as sickness and health are two different aspects of the same order of facts, life, while the sacred and the profane have always and everywhere been conceived by the human mind as two distinct classes, as two worlds between which there is nothing in common.
As our models of the universe have become more sophisticated, they more and more resemble religion.
... between the logic of religious thought and that of scientific thought there is no abyss. The two are made up of the same elements, though inequally and differently developed.
Just as there is no known society without a religion, so there exist none, howsoever crudely organized they may be, where we do not find a whole system of collective representations concerning the soul, its origin and its destiny.
Today, science is our religion. We make statements like "trust the science", "the science is settled". Those that disagree are called "deniers", which is equivalent to "heretics" in Christianity. Their views must be suppressed, they must be punished (fired, cancelled, shunned). So far, no burning at the stake.
Page 369, "...he knows that it is faith that saves".
Search your heart. you know it to be true. Our lives are sustained by faith ... we have faith we will get up in the morning, we have faith we can drive to our destination safely, we have faith that the bridge we drive over will not fall, the list is endless, and in this mortal coil, many of the things we have faith in will fail. We will see that many of the earthly things we have faith in will fail. Even though we see that ... people fail to get up, cars crash and the occupants die, bridges fall, etc
But we still go to sleep, drive our cars, and go over bridges, because we can't live without faith. Even faith in people or things shown to be unfaithful,
So faith saves. John 20:29 Jesus said unto him, “Thomas, because thou hast seen Me, thou hast believed. Blessed are they that have not seen and yet have believed.”