Deloris, new Nun student, taking music classes to Nuns instead of Mary Lazarus, Music teacher & also Nun. so Deloris is saying each Nun should listen to other Nun while singing choir. So Mary Lazarus, who is standing beside them, reacted.
Deloris: You must listen to each other if you're going to be a group.
Mary Lazarus: I knew that.
Deloris: Mary Lazarus, as soon as I walked in the door, I knew that you knew this. Now, you're somebody who's into hard work and discipline, aren't you?
Mary Lazarus: Of course, I'm a nun. Four popes now.
Deloris: Four? Wow