This is often missed by those engaging Roman Catholics. If the canon is the very voice of God and the measuring rod, then it must be that which judges all things, including church history, any alleged "infallible" pronouncements, [T]radition and [t]radition. It can't logically be any other way. It can't be that infallible pronouncements and Tradition measure or rule what the Bible says on anything. The Bible is to measure and rule the church rather than the church measuring and ruling the Bible. If this were reversed, the Bible in effect would no longer be functioning as canon. The church, Tradition, infallible pronouncements, etc., would be functioning as the canon. This is what is meant by the phrase sola ecclesia. I'm not sure who originally coined the phrase, but it is indeed an apt way to summarize the actual Roman Catholic rule of faith or measuring rod. Dr White explained long ago:
What is sola ecclesia? It is the concept that the Roman Church (exemplified in the Papacy especially) is the sole and final authority in all matters. Scripture and Tradition (whatever that is in particular) are subservient to the Church, despite Rome’s protests otherwise. A moment’s reflection demonstrates why this is: Rome claims to define both what Scripture is (the canon), and what Scripture says (interpretation of particular passages, as well as the message of Scripture en toto). Likewise, she claims to be able to determine what is "tradition"... and what this tradition then means. Hence, if you control the definition of both the content and meaning of both Scripture and Tradition and you claim to be infallible as well (meaning you cannot retract what you have decided these things teach and have officially defined these views in the past), the result is inevitable: sola ecclesia. The Church as the final authority in all things.