"True, drink is a pleasant delight," said Jan, as one who repeated a truism so familiar to his brain that he hardly noticed its passage over his tongue; and, lifting the cup, Coggan tilted his head gradually backwards, with closed eyes, that his expectant soul might not be diverted for one instant from its bliss by irrelevant surroundings.
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The sentence should be deleted because it introduces information that is irrelevant to the passage.
The writer should deleted the sentence because it provides background information that is irrelevant to the paragraph.