Conduct, practice, is the proof of doctrine, theory. "If any man will do His will — the will of Him that sent me," said Jesus, "he shall know of the doctrine, whether it be of God or whether I speak of myself" (John vii. 17); and there is a well known saying of Pascal: "Begin by taking holy water and you will end by becoming a believer." And pursuing a similar train of thought, Johann Jakob Moser, the pietist, was of the opinion that no atheist or naturalist had the right to regard the Christian religion as void of truth so long as he had not put it to the proof by keeping its precepts and commandments.

The Tragic Sense of Life (1913) - XI : The Practical Problem