Heretics is one of Chesterton’s most important books. He says that we can’t get away from the fact that we have a general view of existence, whether we like it or not. It affects and involves everything we do. And our general view of things is based on our ultimate view of things. Religion is never irrelevant. This book is not an attack, but a defense, a defense of the claims to have gained a deeper appreciation of Christian Faith through the simple exercise of defending it. He says he never realized the philosophic common sense of Christianity until the anti-Christian writers pointed it out to him.
Heresy, it turns out, is usually a distinct lack of common sense. A heresy is at best a half truth that is exaggerated at the expense of the rest of the truth. The modern world praises science and hygiene and progress. These are all very well and good, but they have been elevated at the expense of larger truths, such as faith and tradition and permanent ideals.
By criticizing moral and artistic relativism, he is defending identifiable and absolute standards.