X. Nevertheless, that we may not seem to shun the question (as if it were insoluble [alytos] by us), we can answer directly that the question puts on a fourfold relation or has reference to four things: (1) the doctrine and faith of the elect, who constitute the church; (2) their persons and condition; (3) the place where they were; (4) the form of government under which They lived and the external worship which they had. As to the first, if we treat of the Christian faith, we say the substance of the things to be believed and done in order to salvation was always in the Scriptures, in the Apostles’ Creed, in the law of God and the Lord’s Prayer, sealed by the sacraments, which by a special providence he willed to preserve always in the church for sustaining the alack, although that doctrine was frequently mixed with various errors. So that we must hear accurately distinguish the substance of faith from the corrupting accidents in doctrine and worship, in the midst of which God knew how to preserve his elect in that purity which was necessary for salvation until the age of the Reformation.
XI. Second, if we trees of the persons themselves (i.e., Of the church properly so called, inasmuch as it denotes the mystical body of Christ, constituted of the elect alone), we say that it subsisted in all the elect who were from the time of the apostles, who is all ages have believed in Christ according to the publicly preached truth of the gospel, who separated the substance of saving doctrine in the public ministry from the errors repeatedly creeping in. These we are no more bound to show to them that Elijah was bound to show the 7000 men who have not bowed their knees to bail, although they were truly in Israel.
XII. The condition of this church was miserable and afflicted, both because it was obscure and destitute of splendor (which was adumbrated by the woman flying into the wilderness [Rev. 12:6], small in number and reduced to great paucity, designated by the “two witnesses” [Rev. 11:3], because they were very few when compared with the multitude of those wandering in error) and because it was partly corrupt, partaking in some measure of the errors of the papacy, although it always retained the foundation of salvation and so seceded from the papacy (if not positively, yet negatively; if not in place still in faith and religion), disapproving of her errors and opposing themselves to them as far as they could.
Francis Turretin, Institutes of Elenctic Theology, 18.10.10–12.