One cold December Saturday, Professor Thomas Long's teenage children asked to go Christmas shopping in New York City. "The best bargains," they said, "are in New York City." Dr. Long agreed to take them and their friends, six teenagers in all, on a shopping trip to that great metropolitan center. "There they were," Dr. Long reflected, "six kids marching through the sleaze of Forty-second Street, wide-eyed with curiosity and wonder, yet trying their best to appear cool and nonchalant." Dr. Long was beginning to wonder if it was a good idea to allow teenagers on their own in New York City.

"Just as I was anguishing about the risk I had taken, I heard the voice of a preacher," Dr. Long recalled. "There behind me on a Times Square street corner was a preacher trying to proclaim the Gospel. Hi…