So...if I'm understanding correctly, you're saying that Williamson would be at odds with Rutherford, but not Durham...right?Dating to I think 1964 or so, Williamson likely had separations such as the forming of the OPC in mind. Interestingly, Rutherford absolutizes on this point (as opposed to Durham), though he almost surely is trying to hem in the congregationalists from separating and if pressed I wonder if he would grant Durham's parish example? He may be speaking of a church broadly (as we would denominations). He adduces no proofs but one can imagine using many of the examples from Scripture already cited on the thread (Corinth, most of the seven churches in Asia, etc.).
CONSIDERATION NINE. There is no just cause to leave a less clean church (if it is a true church), and to go to a purer and cleaner, though one who is a member of no church has liberty of election, to join to that church which he conceives to be purest and cleanest.
And, yes, it was 1964.