Music is one of Matt's passions in life. He loves it, and he's also really good at it. He quickly masters the piano and guitar; the guy can even sing. Matt, is there anything you can't do? But it's about more than talent. Matt feels strongly about music because it's something that sets him apart:
"Funny, I never thought of El Patrón as being musical."
Matt's heart was beating wildly. Was he going to be barred from the room?
"If you're musical, he must be," said [Tam Lin]. "But I guess he never had time to study." (9.43-45)
While Tam Lin assumes that Matt's talent in music means that El Patrón must somehow be talented, too, this is the first time we see Matt as different from El Patrón in a real way. El Patrón never explored any musical talent, so by loving and excelling at it, Matt makes it clear that he's an individual person, not a mere copy.
Let's face it: Matt is dismissed and ignored because he's a clone. Everyone assumes he's less than human, and even the people who love him worry that he might turn out to be exactly as bad as El Patrón. He's got the man's DNA.
But music shows just how different Matt is. Our narrator tells us, "The ability to create music filled him with a joy too large to contain. He forgot where he was. He forgot he was a clone. The music made up for everything – the silent contempt of the servants, Steven's and Emilia's snubs, Tom's hatred" (9.42).
We've got a theory we'd like to try out on you, so tell us what you think. Ready? Okay here it comes: Music is another oasis for Matt. When he's playing the piano, he can express himself and his joy. He can forget the troubles of being El Patrón's copy and be his own boy.