Augustine of Hippo

"Whose mouth is full of cursing and bitterness and deceit" [Psalm 10:7]. For it is a great curse to seek heaven by such abominable arts, and to get together such earnings for acquiring the eternal seat. But of this cursing his mouth is full. For this desire shall not take effect, but within his mouth only will avail to destroy him, who dared promise himself such things with bitterness and deceit, that is, with anger and insidiousness, whereby he is to bring over the multitude to his side. …

Exposition on Psalm 10 ↗

Thomas Aquinas

"Whose mouth." Here he sets forth the progress of malice. And first, in the heart, about which he has already spoken. Second, of the mouth. Third, of deed, "he sits in ambush," etc. Regarding the first, he sets forth two things. The sin of the mouth, which is committed in three ways. Sometimes by cursing God or neighbor, which is to break forth into blasphemy: Is. 1: "They have blasphemed the Holy One of Israel." Sometimes they curse partially, when they are held back by fear. …

Exposition on the Psalms of David ↗

Cassiodorus

His wickedness is described as a two-fold corruption, for in his mouth he will have a blasphemous cursing when he makes the false claim that he is the Son of God. He will also have bitterness when he imposes the death penalty on those who resist him, and he will hand over to punishment whoever refuses to worship him as the deity. He will have these things in his mouth, which he will speak in public. …

Explanation of the Psalms 10:28