So, let’s try to prove that there are no gods.
What is a god? A magical, usually anthropomorphic immortal being. Well, if a god existed, he would have to obey the Law of Identity and would not be allowed to have magic. Nor would he be immortal.
So, no, gods cannot exist. Not if being magical and immortal are essential aspects of being a god.
Since such a being is impossible, he clearly cannot exist. That is why some atheists are so certain that no god can exist. It would be worse than naive to believe an impossible entity could possibly exist.
I am guessing because he prefers people to have faith that he exists, rather than direct evidence. It is not a matter of faith to believe someone exists when you hear them speak directly to you.
Or, it could be because he does not exist and it is easier to fake the written Word of God than the oral equivalent.
Trying to fake the spoken word of God has a few problems…
For one he sounds quite mortal and not divine, unless you have a huge special effects budget. Which was clearly not available at the time Christianity was being created.
You could also have God only speak to certain people. But, that has the obvious problem of you then having to just take their word for it. Not a problem if you are taking all this stuff on faith anyway.
As an atheist, I am going with it just being easier to fake, if you say that he prefers mortals to write his word for him.
Having it in a book also makes it easier, for a few reasons, some of which I will explore, in no particular order.
Firstly, remember that in those days most people could not read. In fact, priests were often some of the only people that could read.
So, if God did not speak directly, then how could they know what God said? They have to consult his book. Who can read it? The priests. This made it very easy for priests to become important and powerful people.
It also makes it easier to maintain their status as mysterious cults. If only the priests can read the Word of God, then they are perceived as holders of knowledge that most people cannot have, which increases their perceived authority.
It also makes it harder for most people to argue with the priests. Imagine that some believers disagreed with the meaning of the religious texts. If God spoke to people, then people could try clear it up with God. At least, they could if he existed.
But, if the Word of God is only in written form and the priests do not want to admit that they are wrong, this is much easier if almost nobody else can read the Word of God. Then they can just tell people what they think the text says and not have to worry about people being able to check for themselves.
So, in short, I believe that the two major reasons why the Christian God and many others do not speak directly to most of their believers and instead speak through holy texts are that:
A) The Gods do not exist and it is thus easier to pretend that they do by using holy texts.
B) Holy texts give priests and their various churches more power and perceived credibility in cultures where most people cannot read the holy texts.