In country and rock music a theme may be repeated several times and only the words change. Sometimes a chorus or refrain is added between verses. Usually these songs last only 3 to 5 minutes. In classical music themes may be repeated but rarely are they unchanged. Consider one of the most repeated pieces in classical music, Ravel’s Bolero. Ravel introduces a theme in C maj., repeats it with a new instrument, then introduces a counter melody in A min. and repeats it. He follows this pattern several times all the while adding instruments with each repetition. Then towards the end he plays the major theme followed immediately by the minor theme then ends with a completely different melody.
In this piece, the main theme begins with the trombone, is repeated up a step with the trumpet and new orchestration, then there is an interlude. At measure 184 it returns with the woodwinds. There is another interlude. Then it appears as a three part fugue, followed by another interlude. Then it reappears at the end with full orchestration.
Although listeners like to hear a familiar tune, classical composers are well advised to keep two axioms in mind. “Never bore.” and,” Variety is the spice of life.”