What does it mean that R.L. asked this question and not Jack? That R.L. is the child that wonders about these kinds of things? Does it mean that he has a greater sense of grace, asking for stories, becoming adept at guitar and painting? R.L. seems to care about these things and appreciate their beauty (their "goodness"/grace?) more than Jack ever does.
If we go along with the idea that Jack, if not the main character, is at least the central character of ToL, perhaps his journey is about realizing that he too has followed the way of nature, like his dad, but perhaps completely by accident. His journey then is to figure a way to find the way of grace, the path that his mother and R.L. followed. It gives us then an idea to tackle about what beauty is in the film- there is beauty in grace, but there's also beauty in nature- the thing of it is that it's how you approach it that matters.
Going into again what I said in class about Dad's music: classical music is a lot like designing a building (see what I did there?). You build it from the ground up and it's a stoic kind of thing. On paper it's all bars and keys and lines, structured and exact. The father reads from sheet music and listens from records from the great classical composers- among them Brahms and Bach. I'm not saying there's not beauty in classical music, because there is, but you're not going to find it by conducting with it or staring at the sheet music of it like Dad does. And Bach's Fugues aren't exactly lullabies.
R.L., when he plays the guitar, doesn't read sheet music. He plays with his father by ear in the piano/guitar scene, and it's interesting how nature and grace overlap in that scene. They coexist harmoniously for a little while, and yet they're still independent of each other. Dad plays by the sheet music and R.L doesn't, but they're playing together.