WCF 25.4.
This catholic Church hath been sometimes more, sometimes less visible. (Rom. 11:3–4, Rev. 12:6, 14) And particular Churches, which are members thereof, are more or less pure, according as the doctrine of the Gospel is taught and embraced, ordinances administered, and public worship performed more or less purely in them. (Rev. 2–3, 1 Cor. 5:6–7)