From the simple standpoint, neither atheism, nor theism are religions. But consider this example of science.
To the hard-working, professional scientist, one who delves into the depths of finding knowledge about the workings of nature, science is a simple thing. To him science amounts to, "What is there? and how do I find it out and the why's of it?"
To the simple scientist or to the layman, Science includes all the engineering and the usage of things developed from the engineering.
In the same way, theism is religion at the same time it is not religion, and so is atheism... and just about anything that people live in their lives, including the public understanding of science. Why? Because there is little knowledge, and much belief that people live by.
The big difference is that while the science guy is trying to find the answer by looking at the evidence, religion say they have the answer in their book and tries to fit the evidence to it. If it doesn't fit, religion doesn't change it's view to fit the evidence like science do, they just say. " it doesn't fit what the book says, so it can't be true"
Religions say that they have the answers to the things that they have the answers to. For example. The Bible tells about the creation of the universe. But it doesn't talk about every blade of grass, or mention every person by name who will ever exist.
Science doesn't have much evidence about the creation (or whatever science tries to suggest takes creation's place). But they talk about it like they know what it is all about. For example, if the Big Bang ever happened, nobody knows, and any scientist could postulate a hundred other things that might take the place of the Big Bang.
Yet, science can investigate many of the blades of grass that religion doesn't talk about individually. And, science can investigate many of the people, both living and dead, that religion only suggests might have existed.
People in both religion and science exaggerate what they know and understand, at times. Yet there are few things in religious writings that express the facts that science finds out as clearly as science does.
One of the things that science and the Christian religion agree on is the fact that God exists. Some of the people in both, science and the Christian religion, suggest that God doesn't exist. The point is this. Pure science mostly expresses little, tiny facts. Pure religion expresses believable doctrine.
You really need to go back and check out, in depth, the things of the Bible, its history, now it came into being, and the strength of it. The faith of the Bible is in Jesus Christ, for the salvation of mankind. What is salvation? We live for a hundred years, maybe, if we happen to be strong. Then we die.
There will be a resurrection of both, the righteous and the unrighteous. The righteous will go to a wonderful, glorious, new life with God. The unrighteous will go to an everlasting death... everlasting because it takes a soul an eternity to die.
What's the difference between the righteous and the unrighteous? Their faith in Jesus-God, the Christ, for salvation to eternal life rather than eternal death. The Bible is the only place you find written info about this.