1. Where does the Bible teach the Catholic doctrine of the pope’s infallibility?
Before you build a biblical case for infallibility, make sure the person you are speaking to knows what infallibility means. To non-Catholic ears, the term may be synonymous with anything from omniscience to sinlessness. Therefore, you may need to explain that infallibility does not mean that the pope is a perfect man or that he’ll always say the right thing at the right time. Rather, it may be best to explain it as a negative charism, meaning that infallibility is something that the Holy Spirit prevents the Church from doing—namely, formally teaching error. It is not that the Church knows all things, but that by the will of God, his Church will always be preserved from error, enabling her to pass on the purity of the apostles’ teaching.
The phrase papal infallibility occurs in Scripture as often as the term Trinity: not once. However, it does not follow from this that biblical proof is lacking. Before delving into papal infallibility in particular, we know that Scripture speaks of the Church as the "pillar and bulwark of the truth" (1 Tim. 3:15). This term "bulwark" isn’t something that we use in everyday conversation, so take a look at what the original Greek means. The word originally written by Paul was hedraioma (o has a line over it), which literally means a foundation. Kittle’s Theological Dictionary of the New Testament explains in its article on edraioma, "A Church is established which protects and defends the truth against the confusion of myths. It gives the faith and thinking of individuals a sure ground in confession. No longer God alone, but also the Church of God, now guarantees the permanence of the aletheia [truth] (first e has a line over it). The steadfastness of faith has now become loyalty to the Church and the confession" (vol. II, p. 364). For a Protestant work, this sounds remarkably Catholic.
The early Christians knew that they could turn to the apostolic teaching of the Church as a norm for the truth (2 Tim. 1:13). For whoever heard the Church heard Christ (Luke 10:16), and Christ cannot teach error. So the question should not be "where is infallibility in the Bible," but where in the Bible is the idea that Christ’s Church would teach error? It seems to be taken for granted that by promising to guide the Church into all truth by the power of the Holy Spirit (John 16:13), Christ would guard his flock from erroneous teaching.
We know from Christ’s words to Peter and to the apostles in Matthew 16 and 18 that there would be a profound and dynamic union between heaven and the teaching authority of the Church. When Jesus said to the apostles, "whatever you bind on earth shall be bound in heaven, and whatever you loose on earth shall be loosed in heaven," he was promising a divine ratification of the Church’s teachings. In the original Greek, the tense of the binding and loosing, "shows that a binding occurs in heaven either prior to or simultaneous with the binding performed on earth. In addition, the Greek verb is in the passive voice which indicates that heaven is receiving the binding, not initiating it" (Robert A Sungenis, "The Precedent for Infallibility," letter to authors, November 1993, 5. As quoted in Jesus, Peter, and the Keys, p. 74).
The only way that God would promise this union with heaven is if he intended to protect his Church from falsehood. After all, God is truth and he would not lead his flock into error, much less allow heaven to be bound by it. With this in mind, Christ prayed that Peter’s faith would not fail (Luke 22:32), built the Church upon him (Matt 16), and ordered him to tend and feed Christ’s sheep (John 21:15-17).
This leadership and union would never pass away, since Christ promised that the gates of hell could never prevail against his Church (Matt. 16:18). If the Church ever taught error, it would cease to be Christ’s Church. Therefore, these words of Christ extend beyond a promise of perpetuity to a promise of infallibility.
2. Didn’t the Church invent the doctrine of infallibility in 1870?
Whenever the Church defines a dogma of the faith, you will always have people assuming that that is the date of the doctrine’s "invention." With this mindset, the divinity of Christ was "invented" in 325, and Christians did not "invent" the union of the human and divine natures of Christ until more than a century after that.
Needless to say, the definition of a doctrine is not synonymous with its invention. This would be similar to saying that the fruit of a tree is no different than its original seed. As a seed is planted and may not reach fruition for years, the doctrines of the faith—such as the personhood of the Holy Spirit—may take many centuries to develop and articulate clearly. But regardless of how long the Church takes to define a particular teaching, it must be present from apostolic times.
Evidence for this with regard to infallibility is not lacking. Almost a century before the divinity of Christ was dogmatically established, Cyprian of Carthage had this to say of the Church, "Would heretics dare to come to the very seat of Peter whence apostolic faith is derived and whither no errors can come" (Epistulae 59 (55), 14, [256 A.D.]).
Prior to this, Irenaeus of Lyons said, "But since it would be too long to enumerate in such a volume as this the succession of all the churches, we shall confound all those who, in whatever manner, whether through self-satisfaction or vainglory, or through blindness and wicked opinion, assemble other than where it is proper, by pointing out here the successions of the bishops of the greatest and most ancient church known to all, founded and organized at Rome by the two most glorious apostles, Peter and Paul, that church which has the tradition and the faith which comes down to us after having been announced to men by the apostles. With that church, because of its superior origin, all the churches must agree, that is, all the faithful in the whole world, and it is in her that the faithful everywhere have maintained the apostolic tradition" (Against Heresies 3:3:2 [A.D. 189]).
In 433 Pope Sixtus III said that "all know that to assent to [the Bishop of Rome’s] decision is to assent to St. Peter, who lives in his successors and whose faith fails not." While there are many other passages from the early Church Fathers that demonstrate the infallibility of the Church, these should suffice to prove that the doctrine was not "invented" in 1870 when Vatican I defined it formally.
3. How could Peter have been infallible if Paul said that he clearly was wrong (Gal. 2:11-16)?
When this passage is read in context, it becomes clear that Paul was not questioning Peter’s teaching, but was admonishing him for failing to practice what he preached. Peter knew full well that Jews are saved in the different manner as the Gentiles, but by leaving table fellowship with the Gentiles, Peter’s actions were hypocritical. For this reason, Paul opposed him to his face, for by his actions he was "not straightforward about the truth of the gospel" (Gal. 2:14).
While this was a sin on Peter’s behalf, it does not infringe upon the gift of infallibility. After all, the Holy Spirit still used him to infallibly write two books of inerrant Scripture. By mentioning this, it is useful to draw a parallel between the inspiration of Scripture and the infallibility of the Church. While they are distinct, the fact that all Protestants accept the inerrancy of Scripture can be used by the Catholic apologist to explain God’s reasons behind infallibility.
If God can take fallible and sinful men (the authors of sacred scripture) and transmit his truth through them without error, why would God not be able to take fallible, sinful men (the pope and bishops), and use them to preserve his teaching without error? This is the only safeguard that his Church has to keep the pure teaching of the apostles from being tainted. Otherwise, we are left with an inerrant document (the Bible), that is used by 30,000 different denominations to justify their contradictory teachings. The fault is not in the Scriptures but in the desire to part with its authoritative interpreter—the Church.
4. Considering the Church’s actions during the inquisitions, how can the Church claim to be infallible?
As was said earlier, perhaps the most common misunderstanding of papal infallibility is to confuse it with impeccability (the inability to sin). The Church has never claimed this for her members. But the fact that some leaders within the Church have committed grievous sins brings up an important point: Can the sinfulness of a particular church leader invalidate the divine institution of Christ Church?
While a tree can surely be known by its fruit, if we were to judge the apostolic Church by the behavior of the apostles on Good Friday, there would be no reason to accept Christ’s Church. Just as the early Christians did not leave Peter because of Judas, the faithful today are not free to leave the Church based upon the faults of any individual. The bottom line is that there is fundamentally only one reason to choose a church: Is it true?
If it is not true, then no matter how good the company is, one should not join. Conversely, even if there are weeds and wheat in the Church, you should remain so long as it is the one Jesus established. Since the Church is more of a hospital for sinners than it is a museum for saints, we should not be surprised when even some esteemed leaders within the hierarchy fall at times. If Jesus called Peter "Satan" a few verses after he said he would build his Church upon him, we can rest assured that Christ’s Church does not stand or fall based upon the perfection of its members.