The church is a structure on the Island near the beach camp which Eko and Charlie were building until Eko found a new purpose in pushing the button in the Swan. Following Eko's movement into the Swan, Charlie attempts to continue work but finds it difficult and gets frustrated with Eko's abandonment of the project.
Eko told Bernard, "People are saved in different ways," in response to Bernard's frustration that they were building a church when he wanted help building an SOS sign. ("S.O.S.")
Locke built his sweat lodge inside the frame of the church. ("Further Instructions")
Eko was building the church for Yemi after killing three men inside his church in Nigeria. As Eko left Nigeria for London, Amina told him that, because of his actions, he owed Yemi a new church. ("The Cost of Living")
Rose was by the church when Ben moved the Island with the frozen wheel. ("Because You Left")
The church can be seen briefly in "Exposé", "Greatest Hits", and "There's No Place Like Home, Part 1".
Charlie has difficulty trying to build the church by himself. ("Two for the Road")