Sentence:  It was the <WSD>motto</WSD> of a bishop eminent for his piety and good works, ... Serve God, and be cheerful. 
Meaning of the word marked with <WSD> tags:  A sentence, phrase, or word, prefixed to an essay, discourse, chapter, canto, or the like, suggestive of its subject matter; a short, suggestive expression of a guiding principle; a maxim.