The deadliest weapon on earth is a firmly held belief.
In times of stress or crisis, many people will (usually unconsciously) perform some sort of ritual, often one learned in childhood - from picking their nose to throwing a full-blown tantrum, or something a little more sophisticated - "laughing it off", getting a headache, taking the fifth amendment, or just shifting the blame.
There is probably not a human on earth that does not have a repertoire of small but important rituals - the way you brush your teeth, tie your shoes, comb your yak, load your rifle, oh no, they can't take that away from you. Not even those who experience the apparent freedom of extreme madness can escape the domination of ritual - they are, poor bastards, often enslaved to it even more fully, as they count their freckles, endlessly align their pencils, dance clockwise to unheard music and mumble mindless mantras at the back doors of midnight.
Some seem not to have even this support system - the ones who either stay completely cool or crack up suddenly and spectacularly. No religion, no loyalties other than self, respect of the need for law but not for its substance, or custodians, and a painful self-awareness and consequent avoidance of risk-taking. An inability to make decisions.
Decision making requires a belief system.
Animals in the wild do not require beliefs, since important choices are instinctive, or mass decisions made by or in favour of the collective.
Pets, however, develop belief systems. Owner equals food, affection, shelter. Look into your dog’s eyes, and know how a monarch feels. Lay down with men and you get up with flea collars.
Man developed belief systems when he first needed to make decisions, store knowledge and account for the unaccountable. He also found it a great way to forgive himself for undertaking the disposal of other men and their beliefs. Society needs beliefs to survive. Holy Books are survival manuals, encompassing all the rituals of diet, cleanliness, mating and behaviours needed for the collective to survive. They usually provide a schedule of membership fees as well.
Why do people join the belief collectives? Because the purpose of every collective, church, congregation, club or chapter is to anticipate and survive the Apocalypse.
If you believe in that sort of thing.