29 Therefore this so vast difficulty, since our enquiry is about religion, God alone can remedy: nor indeed, unless we believe both that He is, and that He helps men's minds, ought we even to enquire after true religion itself. For what I ask do we with so great endeavor desire to search out? What do we wish to attain unto? Whither do we long to arrive? Is it at that which we believe not exists or pertains to us? Nothing is more perverse than such a state of mind. Then, when you would not dare to ask of me a kindness, or at any rate would be shameless in daring, come you to demand the discovery of religion, when you think that God neither exists, nor, if He exist, has any care for us?
What, if it be so great a matter, as that it cannot be found out, unless it be sought carefully and with all our might? What, if the very extreme difficulty of discovery be an exercise for the mind of the inquirer, in order to receive what shall be discovered? For what more pleasant and familiar to our eyes than this light? And yet men are unable after long darkness to hear and endure it. What more suited to the body exhausted by sickness than meat and drink? And yet we see that persons who are recovering are restrained and checked, lest they dare to commit themselves to the fullness of persons in health, and so bring to pass by means of their very food their return to that disease which used to reject it.
I speak of persons who are recovering. What, the very sick, do we not urge them to take something? Wherein assuredly they would not with so great discomfort obey us, if they believed not that they would recover from that disease. When then will you give yourself up to a search very full of pains and labor? When will you have the heart to impose upon yourself so great care and trouble as the matter deserves, when you believe not in the existence of that which you are in search of? Rightly therefore has it been ordained by the majesty of the Catholic system of teaching, that they who approach unto religion be before all things persuaded to have faith.
Source: On the Profit of Believing (New Advent)