What is meant by orthodoxy

There is a great treasure in James Schalls' book Another Sort of Learning. It's a book of various essays about the important learning (not that all learning is not important) that must go on throughout all of our lives. It's one of those wonderful books that the reader can pick up, open at any spot, and profit from and enjoy what's on the page.

This is from his appreciative essay on 2 of G. K. Chesterton's books: Heretics and Orthodoxy:

"What he meant by orthodoxy was substantially what was in the Creeds as the Church understood them. These Creeds are the foundation of our dignity, and our dignity is undermined somehow every time we seek to change one iota of their content. Indeed, the very effort to change them is itself an instrument in the process of weaving or fashioning another sort of man from the one the Creeds describe. Ultimately, to change the man, you must first change the Creeds. That is why thinking is such a perilous occupation, for in changing your mind, you may well end up changing the world. We can be murdered for our beliefs, but we can more easily be destroyed by our doctrines."