Question: At the beginning, what was the old nun trying to do with the cross key in the dark room with the door that says "God ends here"?
Answer: Are you talking about before she opens the door? She's just making the sign of the cross, but using the same hand she's holding the key in.
I'm asking about what she was going to do in the dark room, what her plan was, what the cross key was for.
It was to open the chamber that kept the vial of the blood of Christ so they could try to send Valak back to Hell.
The gateway to the relic was near the state of Mary, and it wasn't located inside the chamber seeing that Burke and Irene found the relic before crossing the passage leading to the chamber with the sign "God ends here." If there's someone who must have known where the relic was, it has to be the abbess. Then, why didn't she take it if she was going to?
From everything I understood, the cross key opened the chamber that had the blood of Christ. The room with the sign "God ends here" was not the chamber I was speaking about. I was only addressing the question about what the key was for.
Answer: The nun was trying to find the relic. The deceased nuns had no actual idea where it was. That's the whole reason Irene was summoned by the Vatican because she had visions about "Mary pointing the way" also the "ghost nuns" more than likely have something to do with her clairvoyance as well.