I don’t agree with everything he says in his advice for students in his Intro to Statistical Computing class, but I like this a lot:

Programming is expression: take a personal, private, intuitive, irreproducible series of acts of thought, and make it public, objective, shared, explicit, repeatable, improvable. This resembles both writing and building a machine: communicative like writing, but with the impersonal, it all-must-fit check of the machine. All the other principles follow from this fact, that it is turning an act of individual thought into a shared artifact — reducing intelligence to intellect