A mystery is a divinely revealed truth whose very possibility before it is revealed cannot be rationally conceived.
After a mystery is revealed its inner essence is incomprehensible. It cannot be fully understood by the finite mind because it is a manifestation of God, who is infinite and therefore beyond the complete grasp of a created intellect.
A mystery is incomprehensible, but it is intelligible. One of the primary duties of a believer is, through prayer, study, and experience, to grow in faith, to develop an understanding of what God has revealed.
The Central Mystery
§ 234 “The mystery of the Most Holy Trinity is the central mystery of Christian faith and life. It is the mystery of God in himself. It is therefore the source of all the other mysteries of faith, the light that enlightens them. It is the most fundamental and essential teaching in the hierarchy of the truths of faith.”
The most central mystery in the hierarchy of truths! God loves us so much that he has revealed to us more than we can understand. But, because we love God so much, we try valiantly to understand as best we can. If we get the Dogma of the Holy Trinity right, it will lead us to the rest of “the faith which was once for all delivered to the saints” Jude 3. If we misunderstand, we will encounter confusion further along the road.
Some Catholics, pressed by tough questions, say, “It’s a mystery, beyond our understanding.” However, in Catholic teaching, a mystery is not unknowable but incomprehensible, a secret truth or plan hidden from the common knowledge of men.
§ 237 God reveals mysteries to us. Rabbi Yeshua speaks of mysteries of the kingdom of God Mt 13:11; Mk 4:11; Lk 8:10 which he disclosed to his shlikhim but not to the crowds who heard them only in parables, “So that they may indeed see but not perceive, and may indeed hear but not understand” Mk 4:12. God always has reasons for revealing to some but not to others, though we may not understand them at the time.
Jews had prayed the Shma since Moses’ time, but our Father emphasized one God, to break their adherence to Egypt’s many false gods. Jews say the Shma is the basis for their belief in one God as opposed to one triune God. Later, fulfilling Isaiah’s Prophecy, some Jews did not follow Rabbi Yeshua.
By comparison, the Ten Commandments can be discerned in our unaided reason. Imagine a community of ten men and ten women. Each man has to constantly defend his woman against the other nine who would like to take her. Eventually, the men will agree on a law, “You shall not commit adultery.”