Augustine of Hippo

"Who speaks the truth in his heart." For some have truth on their lips, and not in their heart. As if one should deceitfully point out a road, knowing that there were robbers there, and should say, If you go this way, you will be safe from robbers; and it should turn out that in fact there were no robbers found there: he has spoken the truth, but not in his heart. For he supposed it to be otherwise, and spoke the truth in ignorance. Therefore it is not enough to speak the truth, unless it be so also in heart. …

Exposition on Psalm 15 ↗

Jerome

He who has practiced no deceit with his tongue: he who has uttered in speech what he has pondered in his mind. Nor has done evil to his neighbor. Some think that a neighbor is a brother, or a fellow townsman, or a kinsman, or a blood relation. But our Lord teaches in the Gospel in that parable, where a certain man went down from Jerusalem to Jericho: a priest passed by, a Levite passed by, and had no pity: a Samaritan passed by, and had pity. And afterward the Lord asks, and says: Which of these was a neighbor? …

Homily 5, on Psalm 14 ↗

Thomas Aquinas

"Nor has he done." Above, the Psalmist treated of the virtuous action that God accepts, enumerating those things by which a man works well in himself; here he enumerates those by which he conducts himself well toward his neighbor. And here, with regard to his neighbor, he asks three things. First, that he not harm him. Second, that he not consent to one who does harm. Rom. …

Exposition on the Psalms of David ↗