Augustine of Hippo

Then follows, "I will exult for Your salvation:" that is, with blessedness shall I be holden by Your salvation, which is our Lord Jesus Christ, the Power and Wisdom of God. Therefore says the Church, which is here in affliction and is saved by hope, as long as the hidden judgment of the Son is, in hope she says, "I will exult for Your salvation:" for now she is worn down either by the roar of violence around her, or by the errors of the heathen. "The heathen are fixed in the corruption, which they made" [Psalm 9:15]. …

Exposition on Psalm 9 ↗

Jerome

We ought to understand the whole psalm as being about the death of the Savior. Finally, that you may know it is spoken of the Savior, it is said of the Jews: 'In this snare which they stretched out, their own foot has been caught.'

Homily 4, on Psalm 9 ↗

Thomas Aquinas

The occasion of exultation is the destruction of enemies who persecute the saints. And they persecute the saints in two ways. First, by violence. Second, by fraud. He says therefore, regarding the first, "the nations are stuck fast" -- from the fact that they prepared slaughter for others, they themselves were slain; and therefore he said "stuck fast," or, according to Jerome, "submerged": because that which is stuck fast is pressed down with violence. …

Exposition on the Psalms of David ↗