1 Lady, worthy to be honoured in Christ with the service due to your rank, and daughter deservedly distinguished, it was very pleasant and agreeable to us that your letter reached us when together at Hippo, so that we might send this joint reply to you, to express our joy in hearing of your welfare, and with sincere reciprocation of your love to let you know of our welfare, in which we are sure that you take an affectionate interest. We are well aware that you are not ignorant how great Christian affection we consider due to you, and how much, both before God and among men, we are interested in you. For though we knew you, at first by letter, afterwards by personal intercourse, to be pious and Catholic, that is, true members of the body of Christ, nevertheless, our humble ministry also was of use to you, for when you had received the word of God from us, “you received it,” as says the apostle, “not as the word of men, but as it is in truth the word of God.” Through the grace and mercy of the Saviour, so great was the fruit arising from this ministery of ours in your family, that when preparations for her marriage were already completed, the holy Demetrias preferred the spiritual embrace of that Husband who is fairer than the sons of men, and in espousing themselves to whom virgins retain their virginity, and gain more abundant spiritual fruitfulness. We should not, however, yet have known how this exhortation of ours had been received by the faithful and noble maiden, as we departed shortly before she took on her the vow of chastity, had we not learned from the joyful announcement and reliable testimony of your letter, that this great gift of God, planted and watered indeed by means of His servants, but owing its increase to Himself, had been granted to us as labourers in His vineyard.
2. Since these things are so, no one may charge us with presuming, if, on the ground of this closer spiritual relation, we manifest our solicitude for your welfare by warning you to avoid opinions opposed to the grace of God. For though the apostle commands us in preaching the word to be “instant in season and out of season,” yet we do not reckon you among the number of those to whom a word or a letter from us exhorting you carefully to avoid what is inconsistent with sound doctrine would seem “out of season.” Hence it was that you received our admonition in so kindly a manner, that, in the letter to which we are now replying, you say, “I thank you heartily for the pious advice which your Reverence gave me, not to lend an ear to those men who, by their mischievous writings, often corrupt our holy faith.”
3. In this letter you go on to say, “But your Reverence knows that I and my household are entirely separated from persons of this description; and all our family follow so strictly the Catholic faith as never at any time to have wandered from it, or fallen into any heresy—I speak not of the heresy of sects who have erred in a measure hardly admiting of expiation, but of those whose errors seem to be trivial.” This statement renders it more and more necessary for us, in writing to you, not to pass over in silence the conduct of those who are attempting to corrupt even those who are sound in the faith. We consider your house to be no insignificant Church of Christ, nor indeed is the error of those men trivial who think that we have of ourselves whatever righteousness, temperance, piety, chastity is in us, on the ground that God has so formed us, that beyond the revelation which He has given He imparts to us no further aid for performing by our own choice those things which by study we have ascertained to be our duty; declaring nature and knowledge to be the grace of God, and the only aid for living righteously and justly. For the possession, indeed, of a will inclined to what is good, whence proceed the life of uprightness and that love which so far excels all other gifts that God Himself is said to be love, and by which alone is fulfilled in us as far as we fulfil them, the divine law and council,— for the possession, I say, of such a will, they hold that we are not indebted to the aid of God, but affirm that we ourselves of our own will are sufficient for these things. Let it not appear to you a trifling error that men should wish to profess themselves Christians, and yet be unwilling to hear the apostle of Christ, who, having said, “The love of God is shed abroad in our hearts,” lest any one should think that he had this love through his own free will, immediately subjoined, “by the Holy Spirit who is given unto us.” Understand, then, how greatly and how fatally that man errs who does not acknowledge that this is the “great gift of the Saviour,” who, when He ascended on high, “led captivity captive, and gave gifts unto men.”
Source: Letters (New Advent)