“The movement of withdrawal and renunciation is a necessary element in every Christian life. ... It is an inevitable answer; but it is also inadequate. ... It is inadequate, for one thing, because it affirms in words what it denies in action; namely, the possibility of sole dependence on Jesus Christ to the exclusion of culture. Christ claims no man purely as a natural being, but always as one who has become human in a culture; who is not only in culture, but into whom culture has penetrated.”