Unlike most languages, Lisp defines how strings can be transformed to Lisp ASTs (s-expressions). In Scheme (which doesn't allow reader macros) this is a safe op

Unlike most languages, Lisp defines how strings can be transformed to Lisp ASTs (s-expressions). In Scheme (which doesn't allow reader macros) this is a safe operation: you can read untrusted input without worry. By contrast, most other languages only have eval() - which takes a string and parses and executes it as code. In Lisp, eval() takes a Lisp list object and executes that.