"Is THAT Biblical?" or "Where is THAT in the Bible?"

As Catholics we are given two sources of revelation. The Sacred Scriptures, or Bible, and Sacred Tradition.

Strictly speaking we shouldn't have to defend everything we do by being able to point to it in Scripture. That said, only the fool would intentionally neglect knowledge of Scripture. There are two reasons for this. St. Jerome said, "Ignorance of Scripture is ignorance of Christ." The other is that with so many "Sola Scriptura" traditions it is nearly impossible to explain that Catholics are Christian if we can't point to Scripture and say, "See! Here it is!"

Many things which come to us from Sacred Tradition are not found explicitly in Sacred Scripture. Many parts of Tradition are attested to, indirectly or by allegory, by Scripture. This would not be sufficient for "Bible Christians" but, it might help them see that it's not totally unfounded to say "Mary was conceived without sin," because we can point to the greeting of the Angel Gabriel, "Hail, full of grace," and deduce from that that if she were "full of grace" that means she had no sin. If she had no sin it happened one of three ways, she was Baptized with the Trinitarian formula which we know was not the case, that she was conceived normally and sanctified in the womb, or that she was conceived without sin. Given her special place as the Mother of God, which is also not spelled out in Scripture, that it must have been from the very moment of her creation that she was spared from original sin.

Why do I bring this up? Because so much of our efforts in catechesis is rooted in the idea that everything has to be found in the Bible. It makes us accidental protestants. We should be able to establish a justification for the idea of Transubstantiation in Scripture, but too much focus on that leads us to neglect to know who, and why, the language of Transubstantiation came to be.