"Church’s lambda calculus and the Turing machine are equally powerful but differ in the fact that Turing machines use mutable state. To this day, there is a rift between functional and imperative programming languages, because of the separation of Church and state."

[I have known the above quote forever, but I can't find an original source]

edit: might be from Guy Steele: "And some people prefer not to commingle the functional, lambda-calculus part of a language with the parts that do side effects. It seems they believe in the separation of Church and state"