The Preaching of the Gospel (Galatians 1:6-9 (LD 31; BC 29)

How do we know a true church from a false church?  The Belgic Confession gives us there marks of the church to distinguish a true church from a false church.  One of these marks is the preaching of the gospel.  Why is this gospel continually peached?  What does Paul say that is so important about this preaching and working this out?