> a big difference that Common Lisp brings to the table is that it has separate namespaces for variables and functions. This may not sound like much but it makes it much easier to write macros (code that writes code) and facilitates compile-time computing.

A little more detail here: it has a lot more namespaces than that. Indeed, you can attach arbitrary different namespaces of things to symbols if you want to.

It turns out that when you're writing macros in Lisp, the majority of what you use from outside the macro are functions and the majority of symbols that you bind and use within the macro are variables, so if you put them in different namespaces, you get rid of the majority of cases where symbols don't do what you were expecting in a macro.

Now, it's not quite all of the cases, and when it does happen, it's a pain to track down. Which is why the Scheme folks spent the effort and complexity on hygienic macros (where the system rewrites all symbols internally to make variable capture impossible). At the time of Common Lisp's creation, multiple namespaces and unhygienic macros were the obvious choice for production code, since there weren't hygienic systems available. Today you can go either way. In terms of research, hygienic is the route to go, as the work over the last couple of years on strongly typed, hygienic systems has shown.