Here are some of its explanations on the subject. Not unlike the gobbledygook which the Org uses to explain such things as "overlapping generation", "personal death cancels a persons sins", "144,000 will become kings as well as priests", "Christ came in 1914, was present for about 5 years, then went away, but will return yet again!"
"The Vatican Council has explained the meaning to be attributed to the term mystery in theology. It lays down that a mystery is a truth which we are not merely incapable of discovering apart from Divine Revelation, but which, even when revealed, remains "hidden by the veil of faith and enveloped, so to speak, by a kind of darkness" (Constitution, "De fide. cath.", iv). In other words, our understanding of it remains only partial, even after we have accepted it as part of the Divine message...... but we cannot attain that fuller knowledge which supposes that the various elements of the concept are clearly grasped.......
All theologians admit that the doctrine of the Trinity is of the number of these. [mysteries] Indeed, of all revealed truths this is the most impenetrable to reason.....the plurality of Persons in the Godhead is a truth entirely beyond the scope of any created intellect.
The Fathers supply many passages in which the incomprehensibility of the Divine Nature is affirmed. St. Jerome says, in a well-known phrase: "The true profession of the mystery of the Trinity is to own that we do not comprehend it"
Only after the Aristotelean system had obtained recognition from theologians was this question thoroughly treated."