The Council of Nicaea (325 AD) was not only a theological event but also a political act of hospitality, where unity and exclusion were negotiated through imperial power. While Christian hospitality emphasizes welcoming the stranger, Nicaea extended hospitality selectively, honoring persecuted bishops while marginalizing theological opponents like the Arians. Emperor Constantine’s role as host and arbitrator illustrates how hospitality served both as a pastoral virtue and a political tool. The council's hospitality consolidated ecclesiastical authority while also weaponizing exclusion against heresy. This paper explores how the politics of hospitality at Nicaea shaped future Church diplomacy and how modern religious institutions face the same tension between openness and doctrinal integrity. By revisiting Nicaea, we reflect on how hospitality remains a site of both inclusion and exclusion in contemporary interfaith and ecumenical dialogue.