Comment by dreamcompiler

That's true but it's not the most important aspect of macros. Macros let you define a new language that describes your problem solution more directly than you can in raw Lisp. In other words they let you create a Domain-Specific Lamguage (DSL). You can create DSLs in other languages too but it's so difficult that it's uncommon. In Lisp it's so easy that DSLs are a primary programming technique.