Martin Luther was a 16th century German cowboy with a one-trick pony called "Gospel." Utterly obsessed with the subject, this firebrand monk once wrote that “the truth of the Gospel is the principal article of all Christian doctrine . . . Most necessary is it that we know this article well, teach it to others, and beat it into their heads continually.” If you went to dinner with this guy, you could depend on coming away with a greater sense of why Jesus matters.