These things I write to you, though I hope to come to you shortly; but if I am delayed, I write so that you may know how you ought to conduct yourself in the house of God, which is the church of the living God, the pillar and ground of the truth. And without controversy great is the mystery of godliness: God was manifested in the flesh, Justified in the Spirit, Seen by angels, Preached among the Gentiles, Believed on in the world, Received up in glory. (1 Timothy 3:14-16)
Paul’s purpose in writing his first letter to Timothy was to give him instructions on how a local assembly and its leadership should function. This verse (1 Timothy 3:15) is commonly cited by Roman Catholics to "prove" the infallibility of the teaching and doctrines of the Roman Catholic Church. The assumption here being that by the process of apostolic succession, the Roman Catholic Church is the church of God and therefore it is "the pillar and ground of truth", which can never error doctrinally.