When men seek to know God, and bend their minds according to the capacity of human weakness to the understanding of the Trinity; learning, as they must, by experience, the wearisome difficulties of the task, whether from the sight itself of the mind striving to gaze upon light unapproachable, or, indeed, from the manifold and various modes of speech employed in the sacred writings (wherein, as it seems to me, the mind is nothing else but roughly exercised, in order that it may find sweetness when glorified by the grace of Christ);— such men, I say, when they have dispelled every ambiguity, and arrived at something certain, ought of all others most easily to make allowance for those who err in the investigation of so deep a secret.
But there are two things most hard to bear with, in the case of those who are in error: hasty assumption before the truth is made plain; and, when it has been made plain, defence of the falsehood thus hastily assumed. From which two faults, inimical as they are to the finding out of the truth, and to the handling of the divine and sacred books, should God, as I pray and hope, defend and protect me with the shield of His good will, and with the grace of His mercy, I will not be slow to search out the substance of God, whether through His Scripture or through the creature.
For both of these are set forth for our contemplation to this end, that He may Himself be sought, and Himself be loved, who inspired the one, and created the other. Nor shall I be afraid of giving my opinion, in which I shall more desire to be examined by the upright, than fear to be carped at by the perverse. For charity, most excellent and unassuming, gratefully accepts the dovelike eye; but for the dog's tooth nothing remains, save either to shun it by the most cautious humility, or to blunt it by the most solid truth; and far rather would I be censured by any one whatsoever, than be praised by either the erring or the flatterer.
For the lover of truth need fear no one's censure. For he that censures, must needs be either enemy or friend. And if an enemy reviles, he must be borne with: but a friend, if he errs, must be taught; if he teaches, listened to. But if one who errs praises you, he confirms your error; if one who flatters, he seduces you into error. “Let the righteous,” therefore, “smite me, it shall be a kindness; and let him reprove me; but the oil of the sinner shall not anoint my head.”
Source: On the Holy Trinity (New Advent)