It is perhaps unfortunate but almost inevitable that the concepts of spirits and gods came about millenia before man learned to think rationally and use the scientific method to acquire testable, verifiable, logically sound knowledge of the world. Ancient humans came up with the concept of spirits to explain things like wind, drought, disease, good or bad fortune, why animals aren't inanimate, etc. Some humans tried to influence these spirits through the use of rituals. When a rain dance failed, it was the dancer's fault, or maybe he just kept doing it until it rained. The successes were remembered, the failures forgotten, and so the rituals were thought to largely work.
Later, in order to give more authority to these concepts, the spirits were given more and more powers until they became what we call gods. Gods need a realm to live in, and the afterlife developed as a means to explain and comfort against death. Still later when the authority of gods spread to the enforcement of morality, the afterlife got divided into heaven & hell, where you went depending on your behavior. And as the authority grew still more, multiple gods fell out of favor and gave way to a single, all-powerful god.
Of course there are still religions like Hinduism and some smaller religions that still worship multiple gods, or even spirits. And in some religions like Buddhism, the afterlife is replaced by the notion of reincarnation, but the basic concept is still the same, because your next life (good or bad) is dependent on your behavior in this life.
Religion actually starts to make sense when viewed as the creation of human minds to serve various purposes like explaining the unexplainable and enforcing morality. Still, I think it's past time that we as a species matured and adopted rational thought as our rule rather than our exception.
P.S. To "G G G G...", if you are in fact an atheist, that is probably the worst reason for being one that I have ever heard.