Michael Horton pens "The Gospel and the Sufficiency of Scripture", a feature this month in Modern Reformation magazine. In it he quotes the best-selling Habits of the Heart, where Robert Bellah and fellow sociologists surveyed religion in the United States. They concluded that it is best described as "Sheilaism," named after one person they interviewed who said that she follows her own little voice. Bellah proposes that every American is the founder of his or her own religion, following the dictates of his or her own heart.
Horton's (very meaty) article wants to focus on the integral connection between the sufficiency of Scripture and the sufficiency of the gospel, but must begin with the reality that the American church is basically millions of different ideas of what scripture and the gospel mean. To the average Christian, Christianity is just the relative way they see Christianity.