GKC wrote "Heretics" in 1905. He was criticized for not setting forth and defending his own philosophy in "Heretics" alongside the views he wrote against. In response to that criticism, Chesterton followed up "Heretics" with "Orthodoxy" in 1909 where he creatively shared his belief in Christian orthodoxy as expressed in the Apostles' Creed.
The things Chesterton said are more powerful in context. I can't provide that with a few pulled quotes. However, they provide a taste of his insight and genius of expression. If you like what you read here, I hope you read his books.
Chapter 1. Introductory Remarks on the Importance of Orthodoxy
But there are some people, nevertheless—and I am one of them—who think that the most practical and important thing about a man is still his view of the universe.
Vigorous organisms talk not about their processes, but about their aims.
Our modern politicians claim the colossal license of Caesar and the Superman, claim that they are too practical to be pure and too patriotic to be moral;
Chapter 2. On the Negative Spirit
The human race, according to religion, fell once, and in falling gained knowledge of good and of evil. Now we have fallen a second time, and only the knowledge of evil remains to us.
Every one of the popular modern phrases and ideals is a dodge in order to shirk the problem of what is good. We are fond of talking about "liberty"; that, as we talk of it, is a dodge to avoid discussing what is good. We are fond of talking about "progress"; that is a dodge to avoid discussing what is good. We are fond of talking about "education"; that is a dodge to avoid discussing what is good.
The modern man says, "Let us leave all these arbitrary standards and embrace liberty." This is, logically rendered, "Let us not decide what is good, but let it be considered good not to decide it."
Chapter 3. On Mr. Rudyard Kipling and Making the World Small
There is no such thing on earth as an uninteresting subject; the only thing that can exist is an uninterested person.
...the moment you love anything the world becomes your foe.
Before long the world will be cloven with a war between the telescopists and the microscopists. The first study large things and live in a small world; the second study small things and live in a large world.
Chapter 4. Mr. Bernard Shaw
Truth, of course, must of necessity be stranger than fiction, for we have made fiction to suit ourselves.
Chapter 5. Mr. H.G. Wells and the Giants
Chapter 6. Christmas and the Aesthetes
Chapter 7. Omar and the Sacred Vine
Happiness is a mystery like religion, and should never be rationalized.
Man cannot love mortal things. He can only love immortal things for an instant.
Chapter 8. The Mildness of the Yellow Press
But if they make any sort of attempt to be politicians, we can only point out to them that they are not as yet even good journalists.
Chapter 9. The Moods of Mr. George Moore
A man who thinks a great deal about himself will try to be many-sided, attempt a theatrical excellence at all points, will try to be an encyclopaedia of culture, and his own real personality will be lost in that false universalism. Thinking about himself will lead to trying to be the universe; trying to be the universe will lead to ceasing to be anything. If, on the other hand, a man is sensible enough to think only about the universe; he will think about it in his own individual way. He will keep virgin the secret of God; he will see the grass as no other man can see it, and look at a sun that no man has ever known.
Chapter 10. On Sandals and Simplicity
Desire and danger make every one simple.
Chapter 11. Science and Savages
Chapter 12. Paganism and Mr. Dickinson
The set out, with admirable sense, to enjoy himself. By the end of his civilization he had discovered that a man cannot enjoy himself and continue to enjoy anything else.
It is one of the deadly fallacies of Jingo politics that a nation is stronger for despising other nations.
This doctrine is sometimes called the doctrine of original sin. It may also be described as the doctrine of the equality of men.
But if we do revive and pursue the ideal of a simple and rational self-completion we shall end - where Paganism ended. I do not mean that we shall end in destruction. I mean that we shall end in Christianity.
Chapter 13. Celts and Celtophiles.
Rome conquered nations, but Ireland has conquered races.
Chapter 14. On Certain Modern Writers and the Institution of the Family
The man who lives in a small community lives in a much larger world. He knows much more of the fierce varieties and uncompromising divergences of men. The reason is obvious. In a large community we can choose our companions. In a small community our companions are chosen for us.
A big society exists in order to form cliques. A big society is a society for the promotion of narrowness.
We do not dislike them (our small community neighbors) because they have so little force and fire that they cannot be interested in themselves. We dislike them because they have so much force and fire that they can be interested in us as well.
Fastidiousness is the most pardonable of vices; but it is the most unpardonable of virtues.
We make our friends; we make our enemies; but God makes our next-door neighbour.
Chapter 15. On Smart Novelists and the Smart Set
A good novel tells us the truth about its hero; but a bad novel tells us the truth about its author.
The more dishonest a book is as a book the more honest it is as a public document.
Chapter 16. On Mr. McCabe and a Divine Frivolity
Mr. McCabe thinks that funny is the opposite of serious. Funny is the opposite of not funny, and of nothing else.
Mr. Bernard Shaw is funny and sincere. Mr. George Robey is funny and not sincere. Mr. McCabe is sincere and not funny. The average Cabinet Minister is not sincere and not funny.
The thing which is fundamentally and really frivolous is not a careless joke. The thing which is fundamentally and really frivolous is a careless solemnity.
In the modern world solemnity is the direct enemy of sincerity. In the modern world sincerity is almost always on one side, and solemnity almost always on the other. The only answer possible to the fierce and glad attack of sincerity is the miserable answer of solemnity.
Science means specialism, and specialism means oligarchy.
Once men sang together round a table in chorus; now one man sings alone, for the absurd reason that he can sing better.
If scientific civilization goes on (which is most improbable) only one man will laugh, because he can laugh better than the rest.
Chapter 17. On the Wit of Whistler
He was one of those people who live up to their emotional incomes, who are always taut and tingling with vanity.
Chapter 18. The Fallacy of the Young Nation
All men, then, are ritualists, but are either conscious or unconscious ritualists. The conscious ritualists are generally satisfied with a few very simple and elementary signs; the unconscious ritualists are not satisfied with anything short of the whole of human life, being almost insanely ritualistic. The first is called a ritualist because he invents and remembers one rite; the other is called an anti-ritualist because he obeys and forgets a thousand.
Apparently, a delusion does not matter as long as it is a materialistic delusion.
All the absurd physical metaphors, such as youth and age, living and dying, are, when applied to nations, but pseudo-scientific attempts to conceal from men the awful liberty of their lonely souls.
Chapter 19. Slum Novelists and the Slums
Men trust an ordinary man because they trust themselves. But men trust a great man because they do not trust themselves. And hence the worship of great men always appears in times of weakness and cowardice; we never hear of great men until the time when all other men are small.
The kind of man who could really express the pleasures of the poor would be also the kind of man who could share them. In short, these books are not a record of the psychology of poverty. They are a record of the psychology of wealth and culture when brought in contact with poverty.
And if we wish to lay a firm basis for any efforts to help the poor, we must not become realistic and see them from the outside. We must become melodramatic, and see them from the inside. The novelist must not take out his notebook and say, "I am an expert." No; he must imitate the workman in the Adelphi play. He must slap himself on the chest and say, "I am a man."
Chapter 20. Concluding Remarks on the Importance of Orthodoxy
...nothing can be more dangerous than to found our social philosophy on any theory which is debatable but has not been debated.
A man cannot be wise enough to be a great artist without being wise enough to wish to be a philosopher.
To know the best theories of existence and to choose the best from them (that is, to the best of our own strong conviction) appears to us the proper way to be neither bigot nor fanatic, but something more firm than a bigot and more terrible than a fanatic, a man with a definite opinion.
Let us, at least, dig and seek till we have discovered our own opinions. The dogmas we really hold are far more fantastic, and, perhaps, far more beautiful than we think.
However, I will find something to represent the chapters above without quotes. The problem is not that Chesterton failed to say anything quotable. The problem is the opposite. He stretches his points so evenly across these chapters that I can't find one thing I want to include over another and I would almost have to include the whole chapter to do it justice.