12 R. You are moved to good effect. For the Reason which is talking with you promises so to demonstrate God to your mind, as the sun demonstrates himself to the eyes. For the senses of the soul are as it were the eyes of the mind; but all the certainties of the sciences are like those things which are brought to light by the sun, that they may be seen, the earth, for instance, and the things upon it: while God is Himself the Illuminator. Now I, Reason, am that in the mind, which the act of looking is in the eyes.
For to have eyes is not the same as to look; nor again to look the same as to see. Therefore the soul has need of three distinct things: to have eyes, such as it can use to good advantage, to look, and to see. Sound eyes, that means the mind pure from all stain of the body, that is, now remote and purged from the lusts of mortal things: which, in the first condition, nothing else accomplishes for her than Faith. For what cannot yet be shown forth to her stained and languishing with sins, because, unless sound, she cannot see, if she does not believe that otherwise she will not see, she gives no heed to her health.
But what if she believes that the case stands as I say, and that, if she is to see at all, she can only see on these terms, but despairs of being healed; does she not utterly contemn herself and cast herself away, refusing to comply with the prescriptions of the physician? A. Beyond doubt, above all because by sickness remedies must needs be felt as severe. R. Then Hope must be added to Faith. A. So I believe. R. Moreover, if she both believes that the case stands so, and hopes that she could be healed, yet loves not, desires not the promised light itself, and thinks that she ought meanwhile to be content with her darkness, which now, by use, has become pleasant to her; does she not none the less reject the physician? A. Beyond doubt. R. Therefore Charity must needs make a third. A. Nothing so needful. R. Without these three things therefore no mind is healed, so that it can see, that is, understand its God.
Source: Soliloquies (New Advent)