36 Wherefore, if either our reasoning or our discourse has in any way moved you, and if you have, as I believe, a true care for yourself, I would you would listen to me, and with pious faith, lively hope, and simple charity, entrust yourself to good teachers of Catholic Christianity; and cease not to pray unto God Himself, by Whose goodness alone we were created, and suffer punishment by His justice, and are set free by His mercy. Thus there will be wanting to you neither precepts and treatises of most learned and truly Christian men, nor books, nor calm thoughts themselves, whereby you may easily find what you are seeking.
For do you abandon utterly those wordy and wretched men, (for what other milder name can I use?) who, while they seek to excess whence is evil, find nothing but evil. And on this question they often rouse their hearers to inquire; but after that they have been roused, they teach them such lessons as that it were preferable even to sleep for ever, than than thus to be awake. For in place of lethargic they make them frantic, between which diseases, both being usually fatal, there is still this difference, that lethargic persons die without doing violence to others; but the frantic person many who are sound, and specially they who wish to help him, have reason to fear.
For neither is God the author of evil, nor has it ever repented Him that He has done anything, nor is He troubled by storm of any passion of soul, nor is a small part of earth His Kingdom: He neither approves nor commands any sins or wickedness, He never lies. For these and such like used to move us, when they used them to make great and threatening assaults, and charged this as being the system of teaching of the Old Testament, which is most false. Thus then I allow that they do right in censuring these.
What then have I learned? What think you, save that, when these are censured, the Catholic system of teaching is not censured. Thus what I had learned among them that is true, I hold, what is false that I had thought I reject. But the Catholic Church has taught me many other things also, which those men of bloodless bodies, but coarse minds, cannot aspire unto; that is to say, that God is not corporeal, that no part of Him can be perceived by corporeal eyes, that nothing of His Substance or Nature can any way suffer violence or change, or is compounded or formed; and if you grant me these, (for we may not think otherwise concerning God,) all their devices are overthrown.
But how it is, that neither God begot or created evil, nor yet is there, or has there been ever, any nature and substance, which God either begot not or created not, and yet that He sets us free from evil, is proved by reasons so necessary, that it cannot at all be matter of doubt; especially to you and such as you; that is, if to a good disposition there be added piety and a certain peace of mind, without which nothing at all can be understood concerning so great matters. And here there is no rumor concerning smoke, and I know not what Persian vain fable, unto which it is enough to lend an ear, and soul not subtle, but absolutely childish.
Far altogether, far otherwise is the truth, than as the Manichees dote. But since this discourse of ours has gone much further than I thought, here let us end the book; in which I wish you to remember, that I have not yet begun to refute the Manichees, and that I have not yet assailed that nonsense; and that neither have I unfolded any thing great concerning the Catholic Church itself, but that I have only wished to root out of you, if I could, a false notion concerning true Christians that was maliciously or ignorantly suggested to us, and to arouse you to learn certain great and divine things. Wherefore let this volume be as it is; but when your soul becomes more calmed, I shall perhaps be more ready in what remains.
Source: On the Profit of Believing (New Advent)