One of the beauties of being a pianist is that we are blessed with a breadth of beautiful repertoire that spans centuries. Another blessing is that because of the richness of the repertoire and the nature of the instrument, pianists are quite self-sufficient and don’t rely on other musicians to realize a piece of music. This is naturally different to the reality of most other instrumentalists, who often require a pianist to partner with onstage.
The simultaneous blessing and curse of being a pianist is that because the piano is a self sufficient instrument, pianists are required to process a high degree of complexity in their music. While we thankfully don’t have to deal with issues of intonation, we deal instead with balancing melody, countermelody, voicing, (and different dynamics for each voice), harmony, effects, architecture, structure, etc. So when we learn and perform a Beethoven Sonata, for example, we are not really playing piano music. Instead we are performing orchestral music on the piano. The same could be argued for all composers.
How do we bring out the different parts of the music and “sound like an orchestra”? The first and foremost is to analyze, be aware of what the composer is presenting, and then prioritize. What is the main melodic line? Where is the counterpoint? If the composer repeats the section verbatim, shouldn’t I bring out something different on the repeat?
How do I play in a way to show the listener the voice-leading of the various lines? An obvious solution is via dynamics; that is, playing one line louder or softer than the other. Another way is via articulation. One line might be legato, and the other detached.
Both of these tools are examples of “voicing”, which simply means the action of bringing out various lines or “voices” simultaneously.
Being a successful pianist, and transitioning to being a real musician requires making these musical decisions, and this only comes with years of study and experience with the various composers. I would estimate that one must study at least three or four works of a composer before he/she begins to draw parallels, find patterns, and then begins to understand that composer’s “language” or “style”.
And the processes a pianist experiences in understanding the music are very similar to those a conductor would face. In orchestral music, different instruments are assigned different voices. It is the conductor’s responsibility to study a score, analyze it, and go through all of the same processes a pianist would, and then communicate these musical ideas to the various “soloists” or instrument groups in the orchestra. The advantage of having an orchestra as your instrument, of course, is the contrasting textures and timbres of the various instruments. Pianists, therefore, essentially, have to imitate these various colors of the orchestra, or even the human voice, if the music is vocally inspired.