Aang was on the second floor when everything involving Katara's entrance into the cathedral happened. He heard pretty much everything. He then came downstairs.
"Katara!"
"Aang!"
"Where's Sokka?"
"Here I am", Sokka said as he snuck up behind them.
"Don't worry Aang, if Frollo thinks he can trap us here he's wrong.", Katara said.
"Don't act irrationally, my child", the archdeacon said as he walked towards them. "You created quite a stir at the festival. It would be unwise to arouse Frollo's anger further."
"How do you know?", Aang asked.
"Because the same thing happened one year ago."
"What do you mean?"
"Come with me."
The archdeacon took the three of them to a back pew. Over the next hour, he told the entire story of Quasimodo and everyone else involved in the events the year prior.
"Where are they now?", Katara asked.
"Right now they're in Rome. They should be back in a few days however."
"So who rings the bells while Quasimodo is gone?", Aang asked.
"Well usually the monks take turns."
"Can I do it? Considering how we're stuck here and how bored we'll probably get?"
"Well...I don't see why not."
Aang now had something to do. He and Sokka ran upstairs fighting over control of which bell tower. Katara wandered around downstairs.
"You seem tense, my child.", the archdeacon said.
"I am. You saw what happened out there. I thought if just one person could stand up to Frollo then-...what does he have against people who are different anyway?"
"You can't right all the wrongs of this world by yourself."
"Yeah we'll no one out there is going to help that's for sure."
"Well, maybe there's someone in here who can."
As the archdeacon walked away Katara turned around and saw a statue of the Virgin Mary holding a young version of Jesus.
Over the next several days, Katara, Aang and Sokka all learned about Christianity, specifically Catholicism, considering the fact that they were in a cathedral. Despite being in another world, Aang was the Avatar still. His status gave him an unexplainably strong physical connection to Christianity's central figures. This connection changed the way he saw the world.
But one thing that didn't change was that they all wanted to escape the confines of the cathedral. They ultimately decided one night and went all in.
