22 Now it has been my wish on this account to say something on this subject, by reason of certain of our brethren most friendly and dear to us, and without willful guilt indeed entangled in this error, but yet entangled; who think, that, when they exhort any to righteousness and piety, their exhortation will not have force, unless the whole of that, wherein they would work upon man that man should work, they set in the power of man, not helped by the grace of God, but put forth by the alone choice of the free will; as though there can be free will to perform a good work, unless set free by the gift of God!
And they mark not that this very thing themselves also have by the gift of God, that with such power they exhort, as to excite the dull wills of men to enter upon a good life, to enkindle the cold, to correct such as are in error, to convert such as are turned aside, to pacify such as are opposed. For thus they are able to succeed in persuading what they would persuade to, or if they work not these things in the wills of men, what is their work? Wherefore speak they? Let them leave them rather to their own choice.
But if in them they work these things, what? I pray, does man, in the will of man, work so great things by speaking, and does God work nothing there by helping? Yea rather, with how great soever power of discourse man may prevail, as that by skill of discussion, and sweetness of speech, he in the will of man implant truth, nourish charity, by teaching remove error, by exhortation remove sloth, “Neither he who plants is any thing, nor he who waters, but God Who gives the increase.” For in vain would the workman use all means without, unless the Creator should work secretly within.
I hope therefore that this letter of mine by the worthy deed of your Excellence will soon come into the hands of such also; on this account I thought that I ought to say something on this subject. Next that both you yourself, and whatsoever other widows shall read this, or hear it read, may know that you make more advance unto the love and profession of the good of continence by your own prayers than by our exhortations; forasmuch as if it be any help to you that our addresses also are supplied to you, the whole must be assigned to His grace, “in Whose Hand,” as it is written, “are both we and our discourses.”
Source: On the Good of Widowhood (New Advent)