Answer:
Know Lanyon's thoughts directly.
Explanation:
As the reader reads along, he follows Lanyon's line of thoughts and can deduce what Lanyon thinks about the situation. Lanyon reasons that if his friend's (Dr. Jekyll) messenger could go to one place then his friend should have been able to go another place.
Even if there was a problem, he still wondered why he should have received the messenger in secret. He drew the conclusion that he had a cerebral disease at hand. The reader can directly see what Lanyon's are.
I think the answer is Erika has learned an important lesson about life
