Probably depends on whom you are asking. For me the essence is (1) having functions or procedures as the basic building blocks, not classes. (2) Having all the utility and higher order functions you need to deal with the functions and procedures first idea. (3) Having a very powerful syntax, that allows great semantic editing and is never ambiguous. Oh and can actually be extended in useful ways, without having to wait for a committee to decide upon "the one syntax to rule them all".