3. The Bible Calls the Church and not the Bible the "Pillar and Ground of the Truth."
It is very interesting to note that in I Timothy 3:15 we see, not the Bible, but the Church – that is, the living community of believers founded upon St. Peter and the Apostles and headed by their successors – called "the pillar and ground of the truth." Of course, this passage is not meant in any way to diminish the importance of the Bible, but it is intending to show that Jesus Christ did establish an authoritative and teaching Church which was commissioned to teach "all nations." (Matt. 28:19). Elsewhere this same Church received Christ’s promise that the gates of hell would not prevail against it (Matt. 16:18), that He would always be with it (Matt. 28:20), and that He would give it the Holy Spirit to teach it all truth. (John 16:13). To the visible head of His Church, St. Peter, Our Lord said: "And I will give to thee the keys of the kingdom of heaven. And whatsoever thou shalt bind upon earth, it shall be bound also in heaven: and, whatsoever thou shalt loose on earth, it shall be loosed also in heaven." (Matt. 16:19). It is plainly evident from these passages that Our Lord emphasized the authority of His Church and the role it would have in safeguarding and defining the Deposit of Faith.
It is also evident from these passages that this same Church would be infallible, for if at any time in its history it would definitively teach error to the Church as a whole in matters of faith or morals – even temporarily – it would cease being this "pillar and ground of the truth." Since a "ground" or foundation by its very nature is meant to be a permanent support, and since the above-mentioned passages do not allow fro the possibility of the Church ever definitively teaching doctrinal or moral error, the only plausible conclusion is that Our Lord was very deliberate in establishing His Church and that He was referring to its infallibility when He called it the "pillar and ground of the truth."
The Protestant, however, has a dilemma here by asserting the Bible to be the sole rule of faith for believers. In what capacity, then, is the Church the "pillar and ground of the truth" if it is not to serve as an infallible authority established by Christ? How can the Church be this "pillar and ground" if it has no tangible, practical ability to serve as an authority in the life of a Christian? The Protestant would effectively deny that the Church is the "pillar and ground of the truth" by denying that the Church has the authority to teach.
Also, Protestants understand the term "church" to mean something different from what the Catholic Church understands it to mean. Protestants see "the church" as an invisible entity, and for them it refers collectively to all Christian believers around the world who are united by faith in Christ, despite major variations in doctrine and denominational allegiance. Catholics, on the other hand, understand it to mean not only those true believers who are united as Christ’s Mystical Body, but we simultaneously understand it to refer to a visible, historical entity as well, namely, that one – and only that one – organization which can trace its lineage in an unbroken line back to the Apostles themselves: the Catholic Church. It is this Church and this Church alone which was established by Christ and which has maintained an absolute consistency in doctrine throughout its existence, and it is therefore this Church alone which can claim to be that very "pillar and ground of the truth."
Protestantism, by comparison, has known a history of doctrinal vacillations and changes, and no two denominations completely agree – even on major doctrinal issues. Such shifting and changing could not possibly be considered a foundation or "ground of the truth." When the foundation of a structure shifts or is improperly set, that structure’s very support is unreliable (cf. Matt. 7:26-27). Since in practice the beliefs of Protestantism have undergone change both within denominations and through the continued appearance of new denominations, these beliefs are like a foundation which shifts and moves. Such beliefs therefore cease to provide the support necessary to maintain the structure they uphold, and the integrity of that structure becomes compromised, Our Lord clearly did not intend for His followers to build their spiritual houses on such an unreliable foundation.