It's different. Macros can change the language grammar (it's like inventing a new way to structure a sentence in English, instead of the usual object-verb-complement). Libraries just provide new vocabularies (new names, new verbs, etc.).
You can use the English language to express ideas on very different topics (food, law, engineering, romance, etc.) without changing its grammar.
But that's the point. When you can't change the grammar, you instead end up writing in a different language that doesn't even have a grammar, and encoding it in the base language plus a bunch of horrible configuration.
Look at Spring for an example.