(Mere Christianity) It is…like a hall out of which doors open into several rooms. If I can bring anyone into that hall, I have done what I attempted. But it is in the rooms, not the hall, that there are fires and chairs and meals. The hall is a place to wait in, a place from which to try the various doors, not a place to live in.
C.S.Lewis, Mere Christianity, pp.11-12
In other words, the originator (?) of Mere Christianity admits that you cannot be a ‘mere Christian’. A church needs specific doctrine and once Christ is confessed we come to matters of the nature of the Sacraments, church discipline, the place of Scripture etc.
On these matters I might take great exception to Lewis’ positions.