Please Explain This Java principle: A program can’t consist of nothing but commands.

Object-oriented programming (OOP) is a programming paradigm based on the concept of "objects", which can contain data, in the form of fields (often known as attributes or properties), and code, in the form of procedures (often known as methods).

If a program has only commands, you’re basically telling it to do things without telling it how, or giving it the data it needs. There has to be some data, some kind of information to pass to those commands for them to work.