The author is so right - the "church" is not a denomination, but a condition of the heart. For those who have received Jesus as Savior and Lord, they have become a member of "the church".
The Mormons also make a statement, "we are the one true church". Which is a bunch of poppy-cock.
The true "church" consists of true believers; be they Methodists, Catholics, Presbyterians, Lutherans, and even us Fundamentalists, etc.