During the late twentieth century Baptist church membership declined whilst church attendance increased. An investigation of these phenomena references Stanley Grenz’s post-foundational theology and Anthony Giddens’s sociological theory of structuration. An historical overview of Baptist church history reveals the continuities and discontinuities in the theology and practice of church membership. Attention is focused on the covenantal discourse of professional theology from the early 1980s to date, on the denominational discourse informing a sample of 120 church membership materials, and on the relational discourse of twenty interviews with church members and attenders. Interview data shows that membership discourses have two forms: formal and relational. The latter is found to reduce distinctions between members and nonmembers for which ‘belonging’ provides a validating framework enforced by four features: experientially-validated subjectivity; post-denominationally conceived identity; de-structured relationality; and practical immediacy. Scripture, church tradition and the contemporary context are the sources for Grenz’s post-foundational theology and point to the trialectical tension between the covenantal, denominational and relational discourses of membership and belonging. A discursive theological methodology is proposed that is located within the congregation, rooted in a trialogue, requires deeper scriptural engagement, and is focussed on discussion of an additional Core Value: ‘relational communities’.