Spirituality is a natural result of self-awareness. The more aware a person is of the mysteries that lurk inside them and in the world around them, the more interested a person will be in spirituality.
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Spirituality is like collecting little porcelain figurines. It's silly, there's no point to it, you can't do anything fun with it or it breaks, it's a waste of time, and it's just a harmless hobby for nice old ladies who smell funny.
Lots of reasons. Sometimes they're instructed to. Sometimes they're tempted to. Sometimes they do it by themselves without realizing that they're engaging in something one might label as "spiritual," sometimes accidentally or by circumstance, and sometimes deliberately, to produce a desired effect.
*Concrete can get boring and meaningless. (even for sensors.) The unknown is always more enticing.
*People like to exist for a purpose instead of just existing for its own sake, and purpose can be found through a spiritual understanding of the world.
*Haven't there been studies for the brain activity of spiritual experiences and how there's certain brain activity? It's probably a pleasure-chemical activation?
*Because if you're being pulled into a spiritual understanding of the world, some metaphorical force has to be acting on you for you to feel that pull. (i.e. there is a god, etc.)
*You don't have a soul. You are a Soul. You have a body.
*Faith is the art of holding on to things your reason once accepted, despite your changing moods.