One of the stock arguments for the Roman Magisterium goes like this: there are uncertainties in the interpretation of Scripture. If you doubt that, just consult any good commentary. Or look at all those dastardly Protestant denominations.
The fatal problem with sola Scripture is that if a passage in Paul is unclear, he's unavailable for comment. You can't ask him for clarification because he's dead. Out of reach. Incommunicado.
Thankfully, the Magisterium rides to the rescue. The pope is a living oracle.
Now, whatever the hypothetical merits of that argument, just compare it to reality. At the time of writing, there's a raging debate within the highest circles of Catholicism on the force of Amoris laetitia, a post-synodal apostolic exhortation by the pope. Bishops, archbishops, and cardinals are ferociously wrangling with each other over the meaning of this pastoral document.
And, as luck would have it, the pope who issued that document is still alive! So why doesn't someone just up and ask him? That's what he's there for, right?
Guess what–they did! Four cardinals asked Pope Francis four questions: the dubia.
Guess what–the pope is stonewalling. He refuses to clarify the intent of Amoris laetitia.
But doesn't that defeat the rationale for a living teaching office? Isn't that what the papacy is for–unlike those benighted Protestants who are stuck with a book by dead authors. So please remind me again of why the papacy is indispensable.