Scripture itself says otherwise. In 2 Thessalonians 2:15, Paul commands believers to 'hold fast to the traditions that you were taught, either by an oral statement or by a letter of ours.' The Bible didn't fall from the sky as a finished product; the Church spent centuries discerning which books belonged in it, guided by the same Tradition skeptics want to discard. The Catechism (CCC 80-82) teaches that Sacred Scripture and Sacred Tradition flow from the same divine wellspring and together make up a single sacred deposit of the Word of God, entrusted to the Church.