One of the greatest difficulties is to keep before the audience's mind the question of Truth. They always think you are recommending Christianity not because it is true, but because it is good. And in the discussion they will at every moment try to escape from the issue ‘True-or False’ into stuff about a good society, or morals, or incomes of Bishops, or the Spanish inquisition, or France, or Poland—or anything whatever. You have to keep forcing them back, and again back, to the real point. Only thus you will be able to undermine...their belief that a certain amount of ‘religion’ is desirable but one mustn't carry it too far. One must keep on pointing out that Christianity is a statement which, if false, is of no importance, and if true, of infinite importance. The one thing it cannot be is moderately important."
God in the Dock, 1945, p. 101. [HT: Arthur K]