Of course, if we were giving men advice as to how they ought to conduct secular cases, either for themselves or for their connections, before the church courts, we would rightly advise them to conduct them quietly as matters of little moment. But we are treating of the manner of speech of the man who is to be a teacher of the truths which deliver us from eternal misery and bring us to eternal happiness; and wherever these truths are spoken of, whether in public or private, whether to one or many, whether to friends or enemies, whether in a continuous discourse or in conversation, whether in tracts, or in books, or in letters long or short, they are of great importance. Unless indeed we are prepared to say that, because a cup of cold water is a very trifling and common thing, the saying of our Lord that he who gives a cup of cold water to one of His disciples shall in no wise lose his reward, is very trivial and unimportant. Or that when a preacher takes this saying as his text, he should think his subject very unimportant, and therefore speak without either eloquence or power, but in a subdued and humble style. Is it not the case that when we happen to speak on this subject to the people, and the presence of God is with us, so that what we say is not altogether unworthy of the subject, a tongue of fire springs up out of that cold water which inflames even the cold hearts of men with a zeal for doing works of mercy in hope of an eternal reward? [On Christian Doctrine, IV.xviii.37]
The Protestant denies that we should do good works in hope of receiving an eternal reward, but St. Augustine affirms that it is a good thing—indeed, something that is to be expected as a result of good preaching. Once again we see that St. Augustine was a Catholic.