Over at Called to Communion, there is a monumental post entitled “Solo Scriptura, Sola Scriptura, and the Question of Interpretive Authority.” It’s six months old at this writing, but the most recent comments (836 at last count!) are only several days old.
Besides the article itself, there are many fine comments. The 760th is from Dr. Michael Liccione, and at the risk of doing injustice to other commenters’ offerings, I think this one is noteworthy. Here's a portion:
God authored the books of the New Testament by means of the authorities of the Church he established–to wit, the Apostles and those who wrote in their name. But that Tradition of which the NT is the most authoritative written record is wider and older than the NT. Hence, the NT can only be adequately understood in the context of that wider and older Tradition. Moreover, Tradition itself can only be properly received and interpreted with the mind of the Church to which it was entrusted. Therefore, it is a necessary condition for interpreting the NT adequately that one identify which visible body counts as “the” Church founded by the Lord, and then choose to conform one’s mind with hers. One can only do that by choosing to submit one’s judgment on matters de fide to those with divinely given authority to speak for and to the whole Church: those who hold and exercise the Magisterium. But such a submission would only be justifiable if in fact the Magisterium speaks with divine authority, and is not giving just its own opinions. Anybody can have opinions, but those are always provisional because always fallible. Divine authority, when exercised, is infallible, and thus its judgments are irreformable.
The NT is “adequate” only when prayerfully read in that context. It is of course possible for a person to simply read the NT on its own and learn a great deal of what’s necessary; in fact, I believe it happens a lot. But partly for the reasons given above, I don’t think it’s possible for anybody to assent by faith to the entire content of the deposit of faith in such a way. The history of Protestantism only confirms that judgment for me; in fact, the broad split between the Lutheran, Reformed, and free-church branches of Protestantism was already evident at the Colloquy of Marburg, a dozen years after Luther nailed his theses to the door. Thus, as St. Thomas had said, it is possible to learn by reading the NT alone much of that which is “of faith”; but unless one submits one’s judgment to that of the bishops in apostolic succession, one does not adhere “by faith” to what one thereby learns. For one has no way of knowing that what one learns is the actual faith of the Church rather than just one’s personal opinions. [Emphasis added]