Recent decades have seen a blurring of the line between extremist movements and mainstream politics, driven by rising sectarian polarization. This development has been linked to digital media, with suggestions that so-called echo chambers may drive political radicalization. To understand the social processes taking place inside such digital spaces, this article draws on Randall Collins and the Durkheimian tradition to develop a theory of discursive community formation. Empirically, we analyze 20 years of discussion on the White Power forum Stormfront, employing natural language processing to study discursive evolution as members become socialized into the community. Our findings suggest that digital media provide space for conversational rituals that instill in people a sense of social membership and intersubjectivity, contained in the elaboration of a shared discourse, within which certain beliefs become sacred and unquestionable. This provides a potential social mechanism linking echo chambers to the rise of sectarian polarization.