Against Two Letters of the Pelagians

For as it is said, “It is man's part to prepare his heart, and the answer of the tongue is from the Lord;” so also is it said, “Open your mouth, and I will fill it.” For although, save by His assistance without whom we can do nothing, we cannot open our mouth, yet we open it by His aid and by our own agency, while the Lord fills it without our agency. For what is to prepare the heart and to open the mouth, but to prepare the will? And yet in the same scriptures is read, “The will is prepared by the Lord,” and, “You shall open my lips, and my mouth shall show forth Your praise.” So God admonishes us to prepare our will in what we read, It is man's part to prepare his heart; and yet, that man may do this, God helps him, because the will is prepared by the Lord.

And, Open your mouth. This He so says by way of command, as that nobody can do this unless it is done by His aid, to whom it is said, “You shall open my lips.” Are any of these men so foolish as to contend that the mouth is one thing, the lips another; and to say with marvellous triviality that man opens his own mouth, and God opens man's lips? And yet God restrains them from even that absurdity where He says to Moses His servant, “I will open your mouth, and I will instruct you what you ought to speak.” In that clause, therefore, where He says, “Open your mouth and I will fill it,” it seems, as it were, that one of them pertains to man, the other to God.

But in this, where it is said, “I will open your mouth and will instruct you,” both belong to God. Why is this, except that in one of these cases He co-operates with man as the agent, in the other He does it alone?