Thomas Aquinas, on Ps 11:2

“Save me, O Lord, for there is now no saint: truths are decayed from among the children of men.”

“Then when he says, "vain things," he sets forth the sign of the failure of holiness; and it is twofold, namely vanity and deceitfulness. The first sign of failure is vanity; and with regard to this he says, "they have spoken vain things," etc. That is vain which has no substance. True things, therefore, under which no vanity lies, are firm. Hence 1 Tim. 1: "The end of the commandment is charity from a pure heart, a good conscience, and an unfeigned faith; from which some, straying, have turned aside to vain talking." Jer. 9: "Let each one guard himself from his neighbor." Gregory: "A vain word is an indication of a vain mind." Likewise, that is vain which is not grasped by the understanding; even superfluous words are vain. Prov. 14: "Where there are many words, there is frequently want." Likewise, that is vain which is not stable; and thus words about temporal things are vain. Jn. 3: "He who is of the earth speaks of the earth." Is. 29: "Your speech shall whisper out of the dust." But to whom do they speak vain things? To their neighbor, to whom they ought to speak the truth. Eph. 4: "Let each one of you speak truth with his neighbor." The second sign of the failure of holiness is deceitfulness; and with regard to this he says, "deceitful lips, with a double heart they have spoken." The doubling signifies a double heart. They show by their mouth that they have one thing, but in their heart they have another. They show sorrow and rejoice; they show love and hate; they feign compassion and exult. Jas. 1: "A double-minded man is inconstant in all his ways." Sir. 2: "Woe to the double heart and the wicked lips."”

Imported from an open dataset — not yet checked against the printed edition.