What I haven't seen anyone mention yet is that syntax exists to concisely express semantics. If you want to give me an immediate feel for your interesting semantics, show me how you express them syntactically.

It may be easier to explain (for instance) Rust's borrow-checker in prose, but if you show me a snippet of code using `&mut`, it'll click for me intuitively that something conceptual and important is happening here. That's why I want an illustrative example at the top of the front page.