Notion of the Church as Yeast

We know what happened to some of the mainline Protestant denominations who are attuned to the opinion polls, so to speak, and trim their sails accordingly as the winds of culture shift.  Instead of serving as the yeast which leavens the cultural lump, they ten to disappear into the culture. By remaining faithful to its original commission, by serving its people with love, especially the poor, the lonely, and the dispossessed, and by not surrendering its doctrinal steadfastness, sometimes even the very contradiction of culture by which it seves as a sign, surely the Church serves culture best.

Walker Percy, Signposts in a Strange Land