Clement of Alexandria

And already clearly David, bearing testimony to the truth, sings, "Let sinners be turned into Hades, and all the nations that forget God." They forget, plainly, Him whom they formerly remembered, and dismiss Him whom they knew previous to forgetting Him. There was then a dim knowledge of God also among the nations.

The Stromata Book 6 ↗

Augustine of Hippo

"Let the sinners be turned into hell" [Psalm 9:17]: that is, let them be given into their own hands, when they are spared, and let them be ensnared in deadly delight. "All the nations that forget God." Because "when they did not think good to retain God in their knowledge, God gave them over to a reprobate mind." [Romans 1:28]

ON THE PSALMS, Psalm 9 ↗

Jerome

We ought to understand the whole psalm as being about the death of the Savior. Concerning the calling of the Gentiles: 'All the nations that forget God.'

Homily 4, on Psalm 9 ↗

Thomas Aquinas

"Let them be turned back." Above, the Psalmist treated the judgment of God with regard to his own adversaries; here he pursues it with regard to the whole human race, and with regard to the evils done everywhere by sinners; and regarding this he does two things. First, by way of prayer, he foretells the judgment of God against the wicked. Second, he sets forth the progress of the wicked, at "Why, O Lord?" etc. Regarding the first, he does two things. …

Exposition on the Psalms of David ↗