The Tubergen Lutheran Scholars made it very clear that the Scripture is clear enough that eanyone could understand it by simply reading the Bible (letter sent to the Patriarch of Constantinople Jeremias II). What are all the authors and preachers doing then?
One has to be truly naive to believe that everything our Lord Jesus Christ said was actually written down! The Apostles absorebd as much as humanly possible of His teachings, but their knowledge, passed on to the succeeding bishops, is what made creating the Christian Bible possible more than 350 years after the Penetecost!
Without the Holy Tradition, no one would have been able to argue what is inspired and what is not inspired Word, and that in itself would have made a Bible as we know it, impossible!
More importantly, the theological concepts of the Holy Trinity, and the Duality of Nature of Lord Jesus Christ, were defined in the first two Ecumenical Councils before the Bible was finalized and canonized!.
Surely, our Protestant brethren realize that the concept of Trinity to which they subscribe fully, and the duality of Christ's Nature, two most important pillars of our faith, are not spelled our or obvious by just reading the Scriptures!
Therefore, the foundation of Christianity, was stablished from the Truth of the Fathers from the Apostles, before the Chrsitian Bible.
Finally, one must ask our Protestant friends, where does it say in the Bible that the Bible is the sole authority for the faithful.
You got it. A Protestant pastor delivering a sermon should simply step up to the pulpit, read some scripture, and then sit down. That's "Bible alone."