Church-going people might know a few spiritual songs, or hymns, at least one verse of a favourite; others might know historic 'spirituals', but many of us are more likely to know secular songs, to belt out along with Adele when we're in the car, or sing with Sinatra in the shower.
the challenge's question is, what's in the heart when we do? Why do we sing what we sing? Why do we memorize the lyrics we do? and why not what we don't? that may be a useful measurement of the heart, of our spiritual well-being.