Certainly religious texts and religious practices admit objective description, but religious beliefs, attested to by texts and practices, are more along the lines of a perspective on objects than they are objects themselves. Not being objects themselves, it is incumbent upon outsiders to actually do the hard work of trying to understand what another perspective of objects might say about the objects of our common human experience.
In other words, you have to admit a very human limitation. If you have gotten as far as admitting the very human reality of the difference between a perspective on objects and the objects themselves, you might as well go the rest of the way and admit that truth of a religious belief fall far short of being something manifestly obvious to everyone possessed of sound mind and body. Nothing, no truth, will ever be self-evident to every person. No matter how hard you try, you will never close the distance between what you think about things and the things themselves. The distance is an infinite one; there will always remain a gap. Only a being like God ever could close it; and last I checked, not of us are able to fill those shoes.
Once this very human limitation is admitted, we can start over by turning the world inside out. The subjective definition of religion, or religious belief, regards, not a discrete set of objects, but a perspective on absolutely everything in existence.
The easiest place to begin an insider's account of religious belief is simply with the the human inclination to think about things, anything, like a computer monitor in front of you, or a desk, or the chair you are sitting on. Now extend the range of your conscious awareness and 'abstract' yourself from your immediate surroundings. These things are most likely contained within a room, which has walls and a door. The room is most likely found in a building containing a good number of other rooms. The building will sit alongside other buildings, within the reasonably well-defined limits of a town or city. Mentally zoom out until you are holding the rather vaguely defined contours of our planet in mind. It's entirely possible to go further, of course, and the process can be repeated wherever you find yourself, though my point should be made.
The point is this: tied into the difference between thinking about things and the things themselves, there is a body always situated here and now, and a mental capacity expanded to embrace an ever wider vista. Between the objective and the subjective, the external and internal forms of perception, there is a radical disjunction. The two are stuck together, they fit into each other, inform each other, and so on. The nearer the scale of your consideration to a bodily human scale of existence, the better defined the mental image becomes. The human scale itself is directly apprehended through the bodily senses, especially of hearing, sight, and touch. The further from a human scale, the more blurry the mental image becomes. What they two sides never do is dissolve into each other. The difference between them is one you will carry around for the rest of your life. In a certain sense, you are the difference: the relation between an 'inner' soul and 'outer' body, relating to itself.
I won't labour this longer than necessary. There's nothing necessary about them--nothing logically compelling. Everyone can distinguish in their own mind between thinking about things and the things themselves, but no one must do so.
If you do think through the distinction, however, the duality of the embodied human being is waiting, even if only indirectly, for you to discover almost everywhere you go among the ancient religions. The human being shares the world with innumerable other beings; but the human being, the philosophers, prophets, and sages of old recognized, also knew they share a world with innumerable other beings.
And whatever name given--call it God, Brahman, Nirvana, Heaven, the Tao, etc.--to that something that explains why there is a world full of things in the first place, it is more like the mysterious depths of conscious thought than it is like the perceptible things human beings think about.
The Tao that can be spoken is not the eternal Tao
The name that can be named is not the eternal name
The nameless is the origin of Heaven and Earth
The named is the mother of myriad things (Tao Te Ching, ch. 1)
There was neither non-existence nor existence then; there was neither the realm of space nor the sky which is beyond. What stirred? Where? In whose protection? Was there water, bottomlessly deep? (Rg Veda 10.129.1)
“For my thoughts are not your thoughts,
neither are your ways my ways,”
declares the Lord.
“As the heavens are higher than the earth,
so are my ways higher than your ways
and my thoughts than your thoughts." (Isaiah 55: 8-9)