Tony Woodlief is quoting Dorothy Sayers:

Apart from a possible one per cent of intelligent and instructed Christians, there are three kinds of people we have to deal with. There are the frank and open heathen, whose notions of Christianity are a dreadful jumble of rags and tags of Bible anecdote and clotted mythological nonsense. There are the ignorant Christians, who combine a mild gentle-Jesus sentimentality with vaguely humanistic ethics–most of these are Arian heretics. Finally, there are the more or less instructed church-goers, who know all the arguments about divorce and auricular confession and communion in two kinds, but are about as well equipped to do battle on fundamentals against a Marxian atheist or a Wellsian agnostic as a boy with a pea-shooter facing a fan-fire of machine-guns.

Note commenter John M point about devotional life vs. service. This is all too convicting.