He meant to make plain to a revengeful man that Josiah had friends and that the attempt to blackmail him would be dangerous.

Lamb was sitting up in bed apparently relieved, and was reading a newspaper.

The moment he spoke Rivers knew that he was a far more intelligent person than the man of yesterday.
Lamb said, "Billy, set a chair for Mr.Rivers.The heat's awful for October." Billy obeyed and stepped out glad to escape.
Rivers said, "No, I won't sit down.

I have something to say to you, and I advise you to listen.

You lied to Billy about the doctor yesterday, and you tried to frighten Josiah into getting you whisky--you lied to him." Josiah had not returned, and now it was plain that he had told the clergyman of the threat.