Considering TBATC as a whole from the perspective of just having finished it, I'm not sure whether it is better or worse than Manalive. It's a little harder to understand, but I think that may be due to subtlety. It's also not as moving, but that's not surprising since it's not about how one man should live, but how a society should run.
The story focuses on the continually frustrated struggle of two Scotchman to have a duel for the honor of the Virgin Mary. One is Mr. Turnbull, a fiery atheist who has never in his life been taken seriously, putting out a little newspaper that continually defies the world with his blasphemies. The other is Evan MacIan, a young Scotchman just come to London to make his way in the world. He's a Roman Catholic, grown up in the wildest parts of the highlands, away from the Presbyterian influence of that country. He's also a Jacobite, and steps into London from an isolation that dates back to that era of rebellion. When he reads in the window of Turnbull's shop that the Mother of God is a common harlot, covering her misdeed with a fanciful mythology, he breaks the shop window in a fury to reach Turnbull, and challenges him to a duel.
However, it's not as easy as it sounds, apparently, to fight a duel in early 20th century England. They must flee magistrates, police, liberal Christians, pagan professors, drunken Gentlemen, and an increasing mutual sense of phileo. The story all ends up in an insane asylum with Dr. Lucifer - and a spectacular miracle.
The story is a warning against the effects of modernism on society, it's a not designed to showcase a debate between Christians and atheists. Turnbull and MacIan are equally protagonists, and by the end of the book, they find themselves on the same side against modernity's proffered insanity. Perhaps it can offer advice for an era in which many people are concerned about the relationship of the Church and the State, though I'm not sure anyone wants to hear what Chesterton has to say. Here is what I think is the point of the book - MacIan is speaking to Turnbull:
That's a good question.
"When I saw that, I saw everything; I saw the Church and the world. The Church in its earthly action has really touched morbid things--tortures and bleeding visions and blasts of extermination. The Church has had her madnesses, and I am one of them. I am the massacre of St. Bartholomew. I am the Inquisition of Spain. I do not say that we have never gone mad, but I say that we are fit to act as keepers to our enemies. Massacre is wicked even with a provocation, as in the Bartholomew. But your modern Nietzsche will tell you that massacre would be glorious without a provocation. Torture should be violently stopped, though the Church is doing it. But your modern Tolstoy will tell you that it ought not to be violently stopped whoever is doing it. In the long run, which is most mad--the Church or the world? Which is madder, the Spanish priest who permitted tyranny, or the Prussian sophist who admired it? Which is madder, the Russian priest who discourages righteous rebellion, or the Russian novelist who forbids it? That is the final and blasting test. The world left to itself grows wilder than any creed. A few days ago you and I were the maddest people in England. Now, by God! I believe we are the sanest. That is the only real question-- whether the Church is really madder than the world. Let the rationalists run their own race, and let us see where they end. If the world has some healthy balance other than God, let the world find it. Does the world find it? Cut the world loose," he cried with a savage gesture. "Does the world stand on its own end? Does it stand, or does it stagger?"



