Oversimplifying can be great at times. In this case, the lambda-calculus model (which is the base for this type of "everything is just a function" approach) is

Oversimplifying can be great at times. In this case, the lambda-calculus model (which is the base for this type of "everything is just a function" approach) is a great model of computation because it is so simple, while being easy to handle /reason about (compared to eg. Turing machines), which is why it is at the base of most computer logic/proof systems