OK, this is all copied and pasted, I admit it. But here is one point: if God didn't leave us someone to keep us from making errors, then how does he know we won't mess everything up?
From a Catholic view, this is why there are so many denominations of protestants. Each thinks they are the correct one, but none have the pope to keep the church from making errors in official teachings. Just our view...
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Christ instructed the Church to preach everything he taught (Matt. 28:19–20) and promised the protection of the Holy Spirit to "guide you into all the truth" (John 16:13). That mandate and that promise guarantee the Church will never fall away from his teachings (Matt. 16:18, 1 Tim. 3:15), even if individual Catholics might.
As Christians began to more clearly understand the teaching authority of the Church and of the primacy of the pope, they developed a clearer understanding of the pope’s infallibility. This development of the faithful’s understanding has its clear beginnings in the early Church. For example, Cyprian of Carthage, writing about 256, put the question this way, "Would the heretics dare to come to the very seat of Peter whence apostolic faith is derived and whither no errors can come?" (Letters 59 [55], 14). In the fifth century, Augustine succinctly captured the ancient attitude when he remarked, "Rome has spoken; the case is concluded" (Sermons 131, 10).
An infallible pronouncement—whether made by the pope alone or by an ecumenical council—usually is made only when some doctrine has been called into question. Most doctrines have never been doubted by the large majority of Catholics.
Pick up a catechism and look at the great number of doctrines, most of which have never been formally defined. But many points have been defined, and not just by the pope alone. There are, in fact, many major topics on which it would be impossible for a pope to make an infallible definition without duplicating one or more infallible pronouncements from ecumenical councils or the ordinary magisterium (teaching authority) of the Church.
At least the outline, if not the references, of the preceding paragraphs should be familiar to literate Catholics, to whom this subject should appear straightforward. It is a different story with "Bible Christians." For them papal infallibility often seems a muddle because their idea of what it encompasses is often incorrect.
Some ask how popes can be infallible if some of them lived scandalously. This objection of course, illustrates the common confusion between infallibility and impeccability. There is no guarantee that popes won’t sin or give bad example. (The truly remarkable thing is the great degree of sanctity found in the papacy throughout history; the "bad popes" stand out precisely because they are so rare.)
Other people wonder how infallibility could exist if some popes disagreed with others. This, too, shows an inaccurate understanding of infallibility, which applies only to solemn, official teachings on faith and morals, not to disciplinary decisions or even to unofficial comments on faith and morals. A pope’s private theological opinions are not infallible, only what he solemnly defines is considered to be infallible teaching.
Even Fundamentalists and Evangelicals who do not have these common misunderstandings often think infallibility means that popes are given some special grace that allows them to teach positively whatever truths need to be known, but that is not quite correct, either. Infallibility is not a substitute for theological study on the part of the pope.
What infallibility does do is prevent a pope from solemnly and formally teaching as "truth" something that is, in fact, error. It does not help him know what is true, nor does it "inspire" him to teach what is true. He has to learn the truth the way we all do—through study—though, to be sure, he has certain advantages because of his position.