The priest's obsession is related to the lady staying in this room. Lucien is unsure whether the lady came from here or from the modern world, but he's sure the priest was obsessed with the modern world just to heal her.
Right… because she was sick, no other medicine could heal her. That's why when the priest heard about the modern world and its advanced technology, he did not hesitate to search for it.
He did not hesitate to inquire about the state of things in the modern world. After confirming that life is good and there are illnesses similar to the lady's that was cured easily, the priest does not hesitate to break his morals and decides to make a contract with the devil to let him enter the modern world.
By then, many years have already passed. Despite being ill, the woman gives birth to the child. The little girl also has a sickness, which is entirely different from what the woman is suffering for.
