The authority of the Scriptures upon which the WCF is based. It is that same authority by which we preach Christ risen every day on FR.
The Assembly consisted of some one hundred and fifty members. Thirty were members of Parliament, the remainder divines, representing the chief parties of English Protestants except that of Archbishop Laud...""The Westminster divines did not, of course, regard the authority of Parliament or of any civil magistrate as essential to the calling of an assembly such as the Westminster Assembly was. In Chapter XXXI, which deals with "Synods and Councils", the divines also said: "As magistrates may lawfully call a synod of ministers, and other fit persons, to consult and advise with, about matters of religion; so, if magistrates be open enemies to the Church, the ministers of Christ of themselves, by virtue of their office, or they, with other fit persons, upon delegation from their Churches, may meet together in such assemblies" (Section II). Nevertheless the Westminster Assembly was actually convened by Ordinance of Parliament.