Institutes of Elenctic Theology by Francis Turretin

The church is called 'the pillar and ground of the truth' (1 Tim. 3:15) not because she supports and gives authority to the truth (since the truth is rather the foundation upon which the church is built, Eph. 2:20), but because it stands before the church as a pillar and makes itself conspicuous to all. Therefore it is called a pillar, not in an architectural sense (as pillars are used for the support of buildings), but in a forensic and political sense (as the edicts of the emperor and the decrees and laws of the magistrates were usually posted against pillars before the court houses and praetoria and before the gates of the basilica so that all might be informed of them, as noted by Pliny, Natural History, lib. 6, c. 28+ and Josephus,? AJ 1.70'71 [Loeb, 4:32'33]). So the church is the pillar of the truth both by reason of promulgating and making it known (because she is bound to promulgate the law of God, and heavenly truth is attached to it so that it may become known to all) and by reason of guarding it. For she ought not only to set it forth, but also to vindicate and defend it. Therefore she is called not only a pillar, but also a stay by which the truth when known may be vindicated and preserved pure andentire against all corruptions. But she is not called a foundation, in the sense of giving to the truth itself its own substructure and firmness. (2) Whatever is called the pillar and stay of the truth is not therefore infallible; for so the ancients called those who, either in the splendor of their doctrine or in the holiness of their lives or in unshaken constancy, excelled others and confirmed the doctrines of the gospel and the Christian faith by precept and example; as Eusebius says the believers in Lyons call Attalus the Martyr (Ecclesiastical History 5.1 [FC 19:276]); Basil distinguishes the orthodox bishops who opposed the Arian heresy bythis name (Letter 243 [70] [FC 28:188; PG 32.908]); and Gregory Nazianzus so calls Athanasius. In the same sense, judges in a pure and uncorrupted republic are called the pillars and stays of the laws. (3) This passage teaches the duty of the church, but not its infallible prerogative (i.e., what she is bound to do in the promulgation and defending of the truth against the corruptions of its enemies, but not what she can always do). In Mal. 2:7, the 'priest's lips' are said to 'keep knowledge' because he is bound to do it (although he does not always do it as v. 8 shows). (4) Whatever is here ascribed to the church belongs to the particular church at Ephesus to which, however, the papists are not willing to give the prerogative of infallibility. Again, it treats of the collective church of believers in which Timothy was to labor and exercise his ministry, not as the church representative of the pastors, much less of the pope (in whom alone they think infallibility resides). (5) Paul alludes here both to the use of pillars in the temples of the Gentiles (to which were attached either images of the gods or the laws and moralprecepts; yea, even oracles, as Pausanius and Athenaeus testify) that he may oppose these pillars of falsehood and error (on which nothing but fictions and the images of false gods were exhibited) to that mystical pillar of truth on which the true image of the invisible God is set forth (Col. 1:15) and the heavenly oracles of God made to appear; and to that remarkable pillar which Solomon caused to be erected in the temple (2 Ch. 6:13; 2 K. 11:14; 23:3) which kings ascended like a scaffold as often as they either addressedthe people or performed any solemn service, and was therefore called by the Jews the 'royal pillar.' Thus truth sits like a queen upon the church; not that she may derive her authority from it (as Solomon did not get his from that pillar), but that on her, truth may be set forth and preserved.

”