Sentence:  Raeburn also quotes Rudi Blesh's rhapsodic praise of “the first recordings of pure New Orleans jazz made in modern times . . . pure, uncommercialized jazz . . . as it sounded in its <WSD>first flushes</WSD> of classicism . . . the music of the men . . . who never lost faith in the pure melody that speaks to the heart." 
Meaning of the word marked with <WSD> tags:  (by extension) The beginning; the period of time when something is first starting.