1 If, Honoratus, a heretic, and a man trusting heretics seemed to me one and the same, I should judge it my duty to remain silent both in tongue and pen in this matter. But now, whereas there is a very great difference between these two: forasmuch as he, in my opinion, is an heretic, who, for the sake of some temporal advantage, and chiefly for the sake of his own glory and pre-eminence, either gives birth to, or follows, false and new opinions; but he, who trusts men of this kind, is a man deceived by a certain imagination of truth and piety.
This being the case, I have not thought it my duty to be silent towards you, as to my opinions on the finding and retaining of truth: with great love of which, as you know, we have burned from our very earliest youth: but it is a thing far removed from the minds of vain men, who, having too far advanced and fallen into these corporeal things, think that there is nothing else than what they perceive by those five well-known reporters of the body; and what impressions and images they have received from these, they carry over with themselves, even when they essay to withdraw from the senses; and by the deadly and most deceitful rule of these think that they measure most rightly the unspeakable recesses of truth.
Nothing is more easy, my dearest friend, than for one not only to say, but also to think, that he has found out the truth; but how difficult it is in reality, you will perceive, I trust, from this letter of mine. And that this may profit you, or at any rate may in no way harm you, and also all, into whose hands it shall chance to come, I have both prayed, and do pray, unto God; and I hope that it will be so, forasmuch as I am fully conscious that I have undertaken to write it, in a pious and friendly spirit, not as aiming at vain reputation, or trifling display.
Source: On the Profit of Believing (New Advent)