By knowing words you do not know the language. What you know is the outside language; the inner language is known by knowing the language of ideas.Hazrat Inayat Khan, The Healing Papers
Meditative practice (i.e. playing your instrument within yourself) has considerable benefits when learning a piece of music; and, incidentally, it can come in really handy whenever you find yourself far away from your instrument for a prolonged period of time. Following the advice of French pianist Jean-Claude Henriot (my mentor when I was a student at the Conservatoire in Évry), I recall making use of this technique in order to prepare for classical piano end-of-year exams/recitals.
All you have to do is choose a notated piece of music that you’ve got memorized and try and play it in your mind as precisely as possible. Hear it in great detail, feel the touch of the piano (this also works for non-pianists: just mentally recall the feeling you experience when playing your particular instrument). For beginner/intermediate pianists, Bach’s Inventions work really well because they consist of only two contrapuntal parts — challenging enough (but not too arduous) to hear simultaneously with the mind’s ear. Of course, you can choose virtually any piece of music. When a passage seems unclear, go back and “replay” it again, (much) slower if necessary. Repeat it as many times as needed, just as you would when you practice on your “real” instrument, until you’re able to hear each note, as well as each item of expression attached to each note, with utmost precision.
This kind of practice certainly requires sharp concentration, and thus works best in a calm environment (I used to go on long walks in the fields near my home in Mennecy to do this). And it might take some time for you to grow accustomed to… But don’t give up! If practiced correctly, the benefits of musical meditation will certainly be felt as soon as you return to the piano (the following day for example — it’s always good to allow some time for the mental exercise to fully sink in). Overall, your knowledge of your chosen piece of music will considerably strengthen. As you rely less on muscle memory and more on your mind’s ear, your memory won’t fail you anymore, and you’ll be able to concentrate on musicality right off the bat.
So the language of ideas cannot be heard by the ears alone, the hearing of the heart must be open for it.Hazrat Inayat Khan, The Healing Papers