After asking Jim to stay and chat, Marlow explains how he wants to help Jim. But Jim doesn't think this is a very good idea, so the two of them argue for a while.
Marlow finally makes his case and says he wants to serve as a character reference for Jim and help him land a decent job.
An overwhelmed Jim can't thank him enough.
More awkwardness ensues, with Jim totally embarrassing Marlow with his gratitude, and then Jim takes off, leaving Marlow alone and pensive.