The riff: Inserted by Mike as an angel and devil quarrel amongst the celestial bureaucracy, with the devil saying “Of course if you’re afraid…”
The explanation: I believe Mike is referring to the devil’s voice pitch and tone more than the actual line in this comparison to the character of Dr. Zachary Smith from “Lost in Space.” In the original 1965-1968 series, Dr. Smith, as played by Jonathan Harris, was the show’s main, bumbling antagonist. He was known for his short temper and propensity to verbally abuse everyone around him, particularly The Robot, in long, alliterative sentences. This is mocked in a different MST3k bit, when Crow does an extended Dr. Smith impression.
Novelty factor: I didn’t actually recognize it when I heard it, largely because I never saw any re-runs of the original “Lost in Space,” nor the 1998 movie. I realize now that most of my knowledge of it is probably from other MST3k references.