23 But you will say, consider now whether we ought to believe in religion. For, although we grant that it is one thing to believe, another to be credulous, it does not follow that it is no fault to believe in matters of religion. For what if it be a fault both to believe and to be credulous, as (it is) both to be drunk and to be a drunkard? Now he who thinks this certain, it seems to me can have no friend; for, if it is base to believe any thing, either he acts basely who believes a friend, or in nothing believing a friend I see not how he can call either him or himself a friend.
Here perhaps you may say, I grant that we must believe something at some time; now make plain, how in the case of religion it be not base to believe before one knows. I will do so, if I can. Wherefore I ask of you, which you esteem the graver fault, to deliver religion to one unworthy, or to believe what is said by them who deliver it. If you understand not whom I call unworthy, I call him, who approaches with feigned breast. You grant, as I suppose, that it is more blameable to unfold unto such an one whatever holy secrets there are, than to believe religious men affirming any thing on the matter of religion itself.
For it would be unbecoming you to make any other answer. Wherefore now suppose him present, who is about to deliver to you a religion, in what way shall you assure him, that you approach with a true mind, and that, so far as this matter is concerned, there is in you no fraud or feigning? You will say, your own good conscience that you are no way feigning, asserting this with words as strong as you can, but yet with words. For you cannot lay open man to man the hiding places of your soul, so that you may be thoroughly known. But if he shall say, Lo, I believe you, but is it not more fair that you also believe me, when, if I hold any truth, you are about to receive, I about to give, a benefit? What will you answer, save that you must believe.
Source: On the Profit of Believing (New Advent)