Across Western Europe, churches face pressing questions about their future use as congregations decline and maintenance burdens grow. This paper searches for new terminology to describe 'hybrid' use and proposes the term 'reciprocal space': a space in which Christian worship remains present but is enriched through dialogue with other functions, which in turn stand in a reciprocal relationship with the architectural building itself. Drawing on official church positions and presenting several examples, the study contrasts the cautious, functionalist stance of the Dutch Catholic bishops (2008) - who prefer conversion or even demolition to avoid profanation - with the more expansive vision of the Flemish bishops (2011-2020), who emphasize concentric layers of meaning: liturgical, personal, and cultural. The Protestant Church in the Netherlands (2021) offers yet another approach, advocating 'leeway' that integrates theological, ecclesiastical, and social dimensions, positioning church buildings as communal hubs extending beyond liturgy alone. The paper situates these positions within the framework of an 'ecology of space,' highlighting how buildings function as relational, reciprocal networks of practices, memories, and affordances. From a theological perspective, it argues that reciprocal spaces embody an incarnational and sacramental logic, reflecting the interwoven relationship of God, Church, and world. Historical precedents, such as cathedrals serving as market halls, demonstrate that multi-use is not a modern innovation but part of an organic tradition in which elements and functions are both lost and gained. Ultimately, the paper calls for policies that recognize not only ecclesial and pastoral perspectives but also the agency of the buildings themselves, opening possibilities for creative, multi-layered uses that sustain both sacred and social significance, while also attending to what may be lost in reciprocal use when re-evaluating these buildings.