<p>Online discussions increasingly encompass religious topics, yet little is known about how polarization in these spaces unfolds or what cultural and discursive mechanisms sustain it. This study explores the interplay between narrative structures and polarization dynamics in two major Reddit communities, r/Christianity and r/Buddhism, across nearly two decades of posts and comments, focusing on both cognitive and affective dimensions. Time-series modelling results show that polarization in Christianity community tends toward self-correction and predictability, while Buddhism displays patterns consistent with self-reinforcing dynamics with higher volatility. Crucially, polarization is not tied to fixed discursive elements but remarkably related to how narratives are interpreted, embedded, and circulated within each community’s distinct ecology. In Christianity, polarization is primarily associated with partisan identity rather than political issues related to race, class, or LGBTQ. Whereas in Buddhism, a more complex mix of cognitive patterns has a greater association than identity cues or emotional tone, which may be related to the emphasis on internal cultivation and philosophical pluralism. These findings suggest that polarization dynamics reflect patterns within narrative and cultural contexts of religious tradition. Practically, the study informs the design of narrative-based tools for monitoring polarization, supports the cultivation of more inclusive communicative forms, and provides insights for interfaith dialogue and platform governance aimed at fostering healthier online publics.</p>