God in the sense of a physical entity in a metaphysical space literally can't exist, but that was never what was intended by the story of God or any other religion, at least not in the sense that religion was in competition with "science". So much of Christianity is really just a mashing together of Jewish moral stories in the OT / Talmud and Neoplatonist philosophy. There's an theory going around, and I don't believe it uncritically, that what we know as the New Testament and much of what is considered "Christian" was Roman agitprop to make up a religion, headed by a group around the Flavian Emperors including Josephus and Greek intellectuals. I don't buy it because if the idea was to try and convert Jews to a made up religion, it clearly failed and the Romans would fight more rebellions in Judea/Palestine anyway, and the majority of converts to Christianity were Gentiles who had a particular Greco-Roman take on the religion. A lot of Christianity was picked up because it was a repudiation of everything the Roman Empire stood for, and it also resembled philosophical ideas that had by that time seeped into the mainstream. So, a lot of things Christians are talking about and believe passionate are a kind of philosophy, which is retold through stories and the figures of the NT. It's why you have a lot of things that are considered highly Christian like the Trinity that aren't actually in the Bible, because a lot of the thinking on God was to figure out a religion that would make familiar philosophical conceits seem true to a new generation. In a way, the Christian God is a repudiation of gods and magic and divination altogether, but philosophically the concept of no god wasn't something that made sense to most people. To reject the idea of God(s) was to have, essentially, no "theory of mind" or ability to understand the world, since they lacked a theory of information or biology or the brain to say that thought was just electrical signals or a pattern in the body, and even such an explanation today doesn't answer philosophical questions about what cognition, sentience, a "soul", and so on actually are. Materialism has a giant problem in explaining subjectivity, without resorting to quasi-religious arguments about the human experience that suggest that human thought and nature are inherently connected. That was the conclusion of a great many philosophers from the 19th century onward, that thought was somehow intrinsic to everything and that would get around the whole God problem. What's actually being argued in the existence of "God" is a theory of mind and an understanding of the self. It's why Genesis as a story of creation is transparently a fable, but the important takeaway from Genesis isn't that God literally created the world in 7 solar days, but that Eve ate the fruit of knowledge and humanity became sinful.
It's a sign of how people have been infantilized that people cannot engage with the concept religion was pointing to without having to believe like children who are incredulous and believe anything put in front of them. Usually, when people got older, their faith in God would change to a more philosophical view, even if it was a crude one. Part of it arises from a scientific view which tried to rationalize god, while forgetting that science as a process can't exist without a philosophical root. It's basically trying to disprove the existence of God with God. The only way you could really conceive of a world without God is to have faith that God doesn't exist, or that "God" as a concept does not comport with how you want to view the universe, which means you would necessarily develop a different theory of mind and thought. You couldn't prove through science that God doesn't exist. You might be able to make a rational argument about God's existence, or His nature, but you're not going to run an experiment in the way you would with a scientific theory. In the religious view, every law you derive from science would just be God's work, and God for whatever reason decided the universe would behave in a way that we could understand with scientific theories, and it would move with remarkable regularity. Indeed, the Christian view specifically is that God doesn't do magic arbitrarily in His creation, and the miraculous is understood as something that was highly improbable and perhaps inexplicable except as evidence of God's plan. Substitute "God" with a scheming philosopher-king and you start to see what a lot of Christianity was actually pointing to, and why it was so important to hold the faith. There's layers and levels when you start digging into the history of these things, and as more people started to think about this whole thing, and as people could actually read the Bible and see it had a lot of strange things in it, the people reading it saw in the Bible things that would be its undoing.
Anyway, "God" doesn't exist in the way most people engaging with the concept believe it exists today, because the concept advanced today in the mainstream is designed to be nonsensical and a kind of mind-virus to ensure that people can't understand the religion, or any other religious concept of God. But God doesn't exist in this philosophical way either, because it's quite transparently a way of masking philosophical ideas that don't have great credibility or explanatory power, and never really did. People turned to the Christian religion because it offered answers to spiritual authority, temporal authority, and gave some moral orientation to people that suggested there was something other than an endless parade of violence and rape, which is basically what classical Empires were and continued to be in practice. The idea in Christianity is that the world was evil, but the afterlife didn't have to be and it was okay to say that all of this madness in the world was wrong, and therefore in some small way your life could be better. In the main, though, Christianity rose in a time of great death and decline, and there's a sense in Christianity that this is actually a good thing because the world was sinful. (The whole thing about Election, unconditional election, and so on, is one of those hints that it wasn't about making the world better and that your efforts were futile, but it would be turned into this idea that a chosen minority could act like the ragingest jackasses because God gave them special permission and they were going to get the pass into heaven, and that it was destiny that they were going to be without sin, but that everyone else were maggots and you might as well throw stones at them, kill them, or do whatever you like to them.) But it's all a rather absurd story if you can stop and think about it, and to someone raised outside of the religion, it's really hard to take it seriously. I could never say with any seriousness that any God exists, let alone that a particular guy in Judea who probably didn't exist was God's incarnation on Earth. If that guy actually did exist, he was a Jew preaching to other Jews and all of his teachings had no application to the Gentiles at all. Maybe in some sense he would have tolerated the Gentiles' existence to the extent other Jews at the time did, which was not very much, but the idea that you could just join up by saying God is great would have been alien, and the teachings of Christianity really illustrate that to be an actual Christian meant being in a really selective group of true believers. Even if I tried really hard, I could never bring myself to believe in any of it as something more than a fable, a very long fable and an important one to understand why the world is what it is, but just a fable at the end of the day.
Really, though, the idea of God in this older sense is almost impossible to conceive as something people lived and did in the past, and realistically few people were ever inducted into the actual religion. If you were a priest, you just mouthed the words and knew the stories, but even the priests didn't seem to get it all that much or particularly care. If you were an ordinary person, very likely you went on believing whatever made sense to you. Realistically, ordinary people believed in folk religions and fables and were never big believers in any of the gods. They only adopted Christianity basically because they had to and it was state-enforced, and they never cared about Roman paganism which had literally less than nothing to offer them. They didn't care about the Satan-worship of Babylon or Egypt either, except again because the leaders made it state-compulsory. They didn't care about the ridicuously large Hindu pantheon and probably hated the Brahmins marching around like assholes every single day for century after century. So what we have right now is this parody of God in various forms, whether it's "God is love and sugar" or "Science is God and I'm super smart, also all social interaction is evil." To actually become an atheist is not easy without going through the first step of recognizing that the gods of mankind are all, in one way or another, a devil worship that has considerable effect on human civilization.
