I think when many people ask why there is ‘no religion’ in The Lord of the Rings, they are really asking about monotheism. Why aren’t they characters monotheistic?
The problem with the religion question in Tolkien, to my mind, has always been that The Lord of the Rings is profoundly infused with ‘religious’ sensibilities, just not the ones preferred by the questioner. In order to gain insight into this, we first need to understand how religion first manifested in the real world.
For some time now, psychologists have been aware of the capacity for human beings to attribute intentionality to inanimate objects. We naturally do this, all the time. In most instances, for example if I spill coffee on myself, I will immediately regain composure and it will be apparent that the spill was either my own fault or an accident, and certainly not the will of the cup.
However, for much of human history, human beings (probably) believed that the cup was, in some ways, exerting its will. How else to explain phenomena? Things want to do something, take some action or whatever.
This is the kind of ‘religious’ experience that is imbued throughout Middle-earth. Things – trees, mountains, rings (especially The Ring), even,perhaps, rocks, feel, think, occasionally talk to each other and exhibit intentionality. They have desires (Caradhras, for some reason, is unwilling to allow the Fellowship to cross it) they have regrets (Legolas ascribes regret to the stones of Eregion, although this might be poetic – we cannot know but it would be unwise to rule out a literal reading) and they carry malicious and hurt feelings (the trees of the Old Forest and Fangorn). Middle-earth is a world awash with intentional agents, and this is one of the reasons it is so powerful and interesting a world to enter into.
Although the hobbits might doubt the existence of a walking tree, it never seems to surprise anyone that the Ring, for example, should have some kind of intentionality or will of its own (this is perhaps exaggerated by the films, although it is there in the books as well). Likewise, the characters quickly cotton on to the fact that the Old Forest is intentionally leading them toward the river. No one looks about and says “this is ridiculous, its just a forest. Trees don’t have nervous systems!” The religion inscribed in the book is, in short, a kind of animistic one. The world itself is imbibed with intentional, creative energy. What need is there for monotheism in such a world?
In this world, monotheism didn’t come about until late in human history. As human tribes, nations and city-states become ever larger, and people found that the wealth they created allowed for surplus thinking time, new kinds of religious ideas developed which eventually ‘culminated’ in various kinds of monotheism. No characters in The Lord of the Rings appear to have internalized such an idea – instead they take the intentional powers of the world for granted. The Elves, it is true, celebrate Elbereth, and even ascribe to her creative powers (the Starkindler) but they never invoke any other gods, let alone Eru.
In a letter, Tolkien calls the Rohirrim ‘monotheists’, but there is no evidence for such a stance in the books. They appear to believe in a kind of pre-Christian hero-afterlife, but that’s about it. They do not invoke, let alone worship, a monotheistic deity.
But! The Silmarillion! Eru! Yep, and that deserves a post all its own.