Thomas Aquinas, on Ps 49:20

“Sitting thou didst speak against thy brother, and didst lay a scandal against thy mother’s son:”

“"Sitting, you spoke against your brother." Here he shows how the sin of the tongue is aggravated by the condition of persons. And first, by the condition of the speaker; second, by the condition of the one spoken against; third, by the condition of the hearers. He says, therefore, "Sitting." It sometimes happens that someone says a bitter word when he is moved and provoked; and this is somewhat tolerable. But when someone with a calm heart, unprovoked, says evil things, this is wicked and detestable. And therefore he says, "sitting," namely at ease. Ps. 68: "Those who sat in the gate spoke against me." From the person of the one spoken against, the sin is aggravated: because if he were speaking against a wicked person, it would be different. But he says, "against your brother." Jer. 9: "Let everyone guard himself from his neighbor." "And against the son of your mother you set up a scandal." Here he shows how the sin is aggravated on the part of those who are scandalized by it, namely the hearers. And therefore he says, "you set up a scandal," namely of others, against your brother. And what he says, "the son of your mother," shows that little ones still nursing are called sons of their mother, and the lowly are scandalized by the evil words that he speaks.”

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