How could the presence of these articles in my house affect either the honour, the sanity, or the life of my flighty colleague?
If his messenger could go to one place, why could he not go to another? And even granting some impediment, why was this gentleman to be received by me in secret? The more I reflected the more convinced I grew that I was dealing with a case of cerebral disease . . . The point of view in the excerpt allows the reader to know Hyde's thoughts directly. Predict an action that Hyde will take. Know Lanyon's thoughts directly. Learn something that Lanyon does not know.
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.
