Of course there are many considerations in forming an interpretation of a piece of music,
the era of its composition, attention to issues of historical style and practice, finding a reliable text to work from, issues of structure, harmony, and counterpoint, and more. But for me, two basic formal features of western classical music that seem too often to be neglected are repetition and development.
As material is repeated, there is the fact that as a repetition, it has two important characteristics for us to acknowledge: the first time you hear something, it is new, and we experience it in just that way, in its unfamiliarity. As it is repeated, it gains in familiarity, yet each repetition has a unique place within the music as it unfolds. As we perform these repeated passages, we have the opportunity to make them unique in a variety of ways. As much or our repertoire shares certain features that derive from nature, principally symmetry and asymmetry, we have the possibility of using these characteristics to both provide variation of expression and in doing so to move the narrative of the piece forward. Most phrases in Beethoven are asymmetrical. This makes it easily possible to inflect a repeated phrase differently, say by phrasing it dynamically up and down or down and up to subconsciously clarify its asymmetry for the listener. We can vary the stresses within the phrase. Think of any sentence you wish to speak and say it repeatedly with an accent on a different word each time. That is the idea. On the cello, we have several additional ways of coloring the sound, as well, bow speed and placement, speed and width of vibrato, for example. Below is a funny example of variety and repetition from the celebration of Shakespeare’s 400 birthday.
In a more serious vein, this from Sir Ian