The excerpt contributes to the theme of fate in that it suggests that Farquhar is wrestling with forces larger than himself.
The fact that he was sure of the malign significance of the strange constellations and the voices he hears, suggests that Farquhar thinks an evil force has interfered in his life to have him killed.
Later in the story, however, we learn that the third part of the story was actually a hallucination that came to him between being thrown from the bridge and the rope breaking his neck, and that Farquhar has indeed died.