54 When, therefore, theologians search and the faithful ask for reasons concerning our faith, it is not for the purpose of founding on them their faith, which has for its foundation the authority of God revealing; yet, as Anselm puts it, "as right order requires that we believe the profundities of the faith before we presume to discuss them with our reason, so it seems to me to be negligence if after we have been confirmed in the faith we do not strive to understand what we believe" ("Cur Deus homo," lib . i. c. 2). And here Anselm means that intelligence of which the Vatican Council speaks (Constit. "Dei filius," cap 4). For, as he shows elsewhere, "although since the time of the Apostles many of our Holy Fathers and Doctors say so many and such great things of the reason of our faith . . . yet they were not able to say all they might have said had they lived longer; and the reason of the truth is so ample and so deep that it can never be exhausted by mortals; and the Lord does not cease to impart the gifts of grace in his Church, with whom He promises to be until the consummation of the world. And to say nothing of the other texts in which the Sacred Scripture invites us to investigate reason, in the one in which it says that if you do not believe you will not understand, it plainly admonishes us to extend intention to understanding, when it teaches us how we are to advance towards it." Nor is the last reason he alleges to be neglected: "In the midst between faith and vision is the intellectual knowledge which is within our reach in this life, and the more one can advance in this the nearer he approaches to the vision, for which we all yearn" ("De fide Trinitatis," Praefatio).
Source: Communium Rerum (Vatican.va)