Here’s one of those verses I never saw for thirty years before becoming a Catholic:
1Tim. 3:14 I hope to come to you soon, but I am writing these instructions to you so that, 15 if I am delayed, you may know how one ought to behave in the household of God, which is the church of the living God, the pillar and bulwark of the truth.
St. Paul here asserts that the Church is “the pillar and bulwark of the truth.” (I accept Bo Reicke’s arguments that the pastoral epistles are genuinely Pauline.)
Can a Calvinist call the Church the “pillar and bulwark of the truth”? I submit: only with difficulty. A Calvinist is much more comfortable calling the Scriptures the “pillar and bulwark of the truth.” But that verse isn’t in the Bible.
What ecclesiology is assumed by the statement “the Church ... [is] the pillar and bulwark of the truth”?
I suggest it entails an ecclesiology in which the Church is a (1) single, (2) visible body.
If the Church wasn’t a single body, it could not serve very well as the “pillar and bulwark” of the truth, because one would not know which of the various churches was teaching the truth.
If the Church wasn’t a visible body, it could not serve very well as the “pillar and bulwark of the truth,” because it could not be identified with certainty, nor could it speak with clarity. An invisible, voiceless Church cannot be the support and defense of the truth.
Therefore, I submit that St. Paul assumes that Church is a single, visible body. His ecclesiology is Catholic.
But everyone is free to contradict me. Share your thoughts in the comments.