My old friend John
The narrator here speaks directly to the reader about John Eames, using this familiar tone to describe a character that he likes well. This is reminiscent of book 14 of Homer’s Odyssey, in which the narrator refers to the swineherd Eumaeus as “you, Eumaeus.” Though these two authors address the characters in somewhat different ways, both use the technique of assuming familiarity with a character in order to show a particular fondness for that character. [EB 2006]
Sources: Homer, Odyssey 14.55 and 165.