In "[The Secret of Father Brown](https://archive.org/details/in.ernet.dli.2015.528506/page/n9/mode/2up)" by G. K. Chesterton, Father Brown said:

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> If you try to talk about a truth that’s merely moral, people always think it’s merely metaphorical. A real live man with two legs once said to me: ‘I only believe in the Holy Ghost in a spiritual sense.’ Naturally, I said: ‘In what other sense could you believe it?’ And then he thought I meant he needn’t believe in anything except evolution, or **ethical fellowship**, or some bilge.
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What's meant here by "**ethical fellowship**", as I don't see anything like it in my search? 

And I didn't get **why** the listener thought Brown meant he needn’t believe in anything except....?