I am a Catholic who believes Sacred Tradition helps to illuminate Sacred Scripture.
Here’s an example of what I mean by Tradition illuminating Scripture: As a Catholic, I believe in the Trinity on the basis of Sacred Tradition. Why do I say that? Because I cannot discern the doctrine of the Trinity from the Bible alone for the simple reason that the word “Trinity” is not even in the Bible. Yet I and everyone else who accepts this Tradition can read the Bible and clearly see the doctrine of the Trinity throughout–from Genesis to Revelation.
Yet if you discard Tradition, and rely only on the Bible, not everyone comes to the conclusion that the doctrine of the Trinity is true. Many religious groups accept the Bible and don’t believe in the doctrine of the Trinity. The Jews don’t. The LDS’s and the JW’s don’t. The Arians didn’t, and they argued from the vantage point of sola Scriptura. The oneness Pentecostals don’t.
The doctrine of the Trinity is a part of Sacred Tradition that is not explicitly taught in the Bible. Those who accept this Tradition, though, will read the Bible in this light. We see the Trinity throughout salvation history–from the Creation story of Genesis to the beginnings of the Church at Pentecost.