I have found the term "truth of faith" in the catechism but I am not finding a definition. Aside from the obvious literal meaning, what is the relationship to doctrine or the point in designating something to be a truth of faith?
The phrase “truth of faith” occurs four times in the Catechism. You might want to take a look at each occurrence to see if context will help clear up your doubts. Here’s where to check: 316, 328, 464 and 2503. From what I see, it is used in each case as a synonym for “revealed truth.” By definition, divine revelation is a surer source of truth than scientific methodology or any other human source of knowledge.
This short article may help you understand the idea of truth in faith in a theological sense. Note that in it theology is considered as separate from the doctrine it supports and analyzes. It is the embodiment of doctrine in lived union with God which provides our human contact with the actual truth of our faith.
I also found this article by then-Cardinal Ratzinger to be enlightening, although his professorial writings can be difficult to penetrate. He speaks of “truth of faith” negatively in §5 to show that it cannot be derived from human sources — in this case, history.
Another important document, Dominus Iesus, mentions “truth of faith” in §21 in such a way that it seems to be a synonym for “dogma.” This is a more “propositional” approach, and I am not sure I like it. But the document was issued over the signature of then-Cardinal Ratzinger, so I’m sure there must be something to it.
