What is the point of a lecture when you have a textbook?
I started writing a post about all the things I like to do that the book doesn't: offer an intuitive overview, a fresh perspective on the basics, etc. 

Then I realized that of course, there's no reason that the book couldn't do these things. Most of them don't, but there's no fundamental reason not to. Everything I do in a lecture to help students see the subject from all sides could be translated to the book.

So I guess the main point of lectures is just that it's another medium. Yes you could learn from only one medium, but it goes faster if you use multiple media at the same time. Not just books and lectures: websites, games, audiobooks, documentaries, programming, role playing. Each medium has it's own slight advantages, and idiosyncracies. Even if the story is the same, the energy you have to put in, the mixture of senses you use, and the parts of your brain you activate are all different.

So what, specifically, are the benefits of the medium of a lecture? Here's what I can think of:


Obligation: You are expected to be there. It may be childish, but for a lot of students, it's difficult to work if someone isn't making them do it.
Interaction: It's not just that students are able to ask questions: lecturers can ask te audience a question too. And even if you're not the one answering, you're definitely checking in your head whether you know the answer, which means you're interacting with the material. A book can do this too, ask a reader to consider a question: but the sense of stress isn't there.
Intonation, rhythm and storytelling: A good speaker can hold the attention of an audience. If you're reading, you have to do all the work to keep the attention. The author simply has fewer tools to keep you interested.
Presence The fact that there's an actual person present in the same room as you, makes you sit up. This is a simple human convention. As most lecturers know, it's a convention that students find easy to dismiss, but the basic sense that you're in a room with another person still changes the energy.
Speaker guidance A good speaker will sense the energy of the room. This lets her change speed, take a break, or spend a bit longer on a subject if she notices the room isn't following along. This makes each lecture tailored to the audience. The smaller the audience, the more different the lecture from audience to audience.


Of course, it takes a special lecturer to understand these points and try to capitalize on them. Many don't and just follow the book.