"Maybe he still lacks a little sense of security and doesn't trust you all?" Lumian was very involved and eager to help guess, "Can't you judge based on the content of the letter?"

What he wanted to know more was what the letter was about.

If the target is the church priest and the group, then he is happy to see the success, but if it involves Aurora, he has to urge his sister to move. After all, Aurora often communicates with "pen pals". If caught, she might be involved, and the clues are those letters.