In the first story of the collection, Eliza, the sister of Rev. James Flynn, tells everyone about the beginning of his madness: "It was that chalice he broke."
Well, actually an altar boy that the priest was supervising broke it, but the priest was never the same afterwards; he was "so nervous" he couldn't perform his duties (The Sisters.68). Now, we're sure that's not exactly the biggest bummer ever. But still, it really sticks in the priest's craw. So it seems kind of cruel and humiliating that he winds up buried in a coffin with—you guessed it—a chalice. If you lost the championship basketball tournament because you slipped on a banana peel, you wouldn't to spend eternity with that banana peel would you?
To be fair, though, this is no ordinary cup. A chalice is one of the most holy articles in the Catholic mass. At the very end of the service, the most holy and sacred moment is called the Eucharist. That's when Catholics eat a small piece of bread and drink a sip of wine, believing that at the very moment they consume it, it turns into the actual body and blood of Christ. The chalice contains this wine, so it's really not okay to drop it or break it.
But wait a second. If you were paying close attention, you remember that the chalice Rev. Flynn breaks is actually empty. None of the sacred wine spilled. No blood, no foul, right? Everything's cool, right?
Wrong. It actually might be worse that the chalice is empty. That's because it reminds us that the person responsible for breaking it, Rev. Flynn, is sort of empty, too. Like the chalice, his job is to do something sacred and holy. But he can't do it: he's hollow and fragile and old, and maybe even a little bit insane. Once he breaks the chalice, he knows that he'll break, too.
The fact that the broken chalice comes back as an "idle chalice" for the priest's body may also suggest a larger meaning for the story. It's the first evidence in Dubliners that religion is a dangerous and deceptive force. Not only does the chalice cause the priest's madness, it comes back to taunt his dead body.
And we can even take his one step further: he broke a chalice, but the one on his body isn't broken. By pretending that the chalice was never broken at all, and that Rev Flynn wasn't a broken chalice himself, the official version of events is just a cover up for what really went down. As readers, we know the real story from the sisters, and we can see that the chalice on his body is a cheap way to cover up the tragedy of the priest's life.