Psalms 14:2

31. Thus then what is written, “The mouth that lieth, slayeth the soul;” of what mouth it speaketh, is the question. For in general when the Scripture speaks of the mouth, it signifies the very seat of our conception in the heart, where is approved and decreed whatever also by the voice, when we speak the truth, is uttered: so that he lieth with the heart who approveth a lie; yet that man may possibly not lie with the heart, who uttereth other than is in his mind, in such sort that he knows it to be for the sake of avoiding a greater evil that he admitteth an evil, disapproving withal both the one and the other. …

2. Perceivest thou not how much this reasoning aideth the very persons whom as great game we make ado to catch by our lies? For, as thyself hast shown, this is the sentiment of the Priscillianists to prove which, they apply testimonies from the Scriptures exhorting their followers to lie, as though by the examples of Patriarchs, Prophets, Apostles, Angels; not hesitating to add even the Lord Christ Himself; and deeming that they cannot otherwise prove their falsehood truthful, unless they pronounce Truth to be a liar. It must be refuted, this; not imitated: nor ought we to be partners with the Priscillianists in that evil in which they are convicted to be worse than other heretics. …

14. Wherefore, that which is written, “Who speaketh the truth in his heart,” is not so to be taken, as if, truth being retained in the heart, in the mouth one may speak a lie. But the reason why it is said, is, because it is possible that a man may speak with his mouth a truth which profiteth him nothing, if he hold it not in his heart, that is, if what he speaketh, himself believe not; as the heretics, and, above all, these same Priscillianists do, when they do, not indeed believe the catholic faith, but yet speak it, that they may be believed to be of us. They speak therefore the truth in their mouth, not in their heart. …

Having premised these remarks, let us carefully attend to the passages which he whom we are answering has produced, as if we ourselves had quoted them. “In Deuteronomy, ‘Thou shalt be perfect before the Lord thy God.’ Again, in the same book, ‘There shall be not an imperfect man among the sons of Israel.’ In like manner the Saviour says in the Gospel, Be ye perfect, even as your Father which is in heaven is perfect.’ So the apostle, in his second Epistle to the Corinthians, says: ‘Finally, brethren, farewell. …

2. “He who walketh without stain, and worketh righteousness” ( ver. 2 ). Here he has laid down the proposition; in what follows he sets it forth in detail.

61. So that one may rightly say that the Holy Spirit has this day told us by the voice of the boy reader: “He that is innocent in his hands and of a clean heart, who hath not lifted up his soul to vanity, nor used deceit unto his neighbour, this is the generation of them that seek the Lord.” He, then, shall both ascend into the hill of the Lord and dwell in the tabernacle of God; because “he hath walked without spot, he hath worked righteousness, he hath spoken truth, he hath not deceived his neighbour;” nor did he lend his money for usury, who always wished [no more than] to retain that which was inherited.