the way devi engages with her heritage is an important part of the text because anything that helps make up devi's identity - or crisis of the same - enhances the bildungsroman nature of the story. it's also hugely important for the way it establishes the tension in devi and nalini's relationship.
from the very first scene, mother and daughter are at odds over the value of being indian. devi is praying to their gods, sure, but she's asking for a more classic american teen high school experience. she wants to go to parties and have boyfriends but less body hair. she eats meat with abandon.
(sidebar, but i've always found this quiet, subtle bit of storytelling fascinating -
nalini and mohan are clearly at odds, too, about how heritage should fit into devi's upbringing. mohan feels a certain amount of pride/amusement/affection over devi being all-american, yet nalini disapproves and is even disgusted that this bit of ingrained respect for animals is being violated by her family.)
devi's textbook, then, is imbued with narrative significance where this through line is concerned by the following exchange:
nalini: devi, are you still praying? our gods have other stuff to do, you know?
devi: i was about to ask for good grades.
nalini: now, grab your textbooks. we need to go.
nalini: devi, that textbook has been blessed. if it touches the ground, i have to take it back to the priest. i don't have time to go to rancho cucamonga today!
it wouldn't be apparent to first-time viewers, necessarily, but there's a frustration at the lack of responsibility here that becomes indicative of their season one dynamic, right? nalini wants devi to take praying seriously, she wants her to take the blessed textbook seriously, and she doesn't have the capacity to patiently guide devi toward valuing that seriousness. she herself is grieving and working a demanding job that supports her family and expending more time than she really has to assert the importance of their culture's rituals on devi's life has put a strain on their relationship.
of course, on devi's side of things, she feels this pressure from her mom and the pressure to be accepted by her peers as diametrically opposed forces in her life. being indian only ever alienates devi from american normality, which is why kamala straddling both worlds with what devi perceives as effortlessness gets under her skin so easily.
the show further weaves these threads together - nalini's desire for devi to have a closeness with and respect for her culture and devi's tetchiness over letting her mom down being at odds with her need to be seen as normal - using the textbook in the following dialogue.
devi: how long is kamala gonna stay with us?
nalini: as long as it takes for her to finish her studies. why?
devi: she's just so... [with embarrassment and mild disgust] indian.
devi: like, the other day, she said she was gonna open the tv instead of turn on the tv.
nalini: devi, she is family. she's bettering her life, you could actually learn a little bit from her.
the way devi handles the blessed textbook symbolizes a disconnect with their culture for nalini, and nalini's focus on how it nearly touched the ground even though it didn't symbolizes an impossible standard she'll never be able to meet for devi.
it's obviously significant, then, that at the emotional climax of the episode, devi flings the textbook out of her window.
she's been made to feel fragile by her closest friends who, let's be real, devi was taking comfort in being cooler/more normal than up until the moment she finds out about eleanor's boyfriend. stressed about the way this sets back her misguided plan to paint over her grief with a shiny coat of popularity, devi lashes out at the symbol of these conflicting pressures on her life. she's never more at a loss about her own identity than when she smashes the window with the blessed textbook and lets it hit the ground.
but you know what? that complete lack of control motivates devi to seek out an actually healthy outlet for her emotions, i.e. a talk with her therapist. devi starts rebuilding herself immediately, and that tenacity and strength of spirit is something nalini will acknowledge as a pillar of her daughter's identity when standing up to rhyah two seasons from now.