WCF 25.5.
The purest Churches under heaven are subject both to mixture and error; (1 Cor. 13:12, Rev. 2–3, Matt. 13:24–30, 47) and some have so degenerated as to become no Churches of Christ, but synagogues of Satan. (Rev. 18:2, Rom. 11:18–22). Nevertheless, there shall be always a Church on earth to worship God according to His will. (Matt. 16:18, Ps. 72:17, Ps. 102:28, Matt. 28:19–20)