Macros are how lisps accomplish metaprogramming. You’ll see a lot of people treat lisp macros with a kind of mystical reverence. “Macros allow you to do things that aren’t possible in other languages” is a common refrain, but that’s nonsense. (Turing tarpits exist; other languages have macros.) The difference is that lisps allow you to write programs using the same notation you use for data structures. It’s not that these things are impossible in other languages; it’s just that the lisp way flows seamlessly instead of feeling arcane.