Gregory the Dialogist

In his days the last shall be astonied, and horror shall seize on the first. For he will then let himself loose against the righteous with such a measure of iniquity, that even the hearts of the very Elect shall be struck with no small consternation. Whence it is written, Insomuch that if it were possible, they shall deceive the very Elect. Which, clearly, is said, not because the Elect shall fall, but because they shall tremble with terrible alarms. …

Morals on the Book of Job, Book XIV ↗

Thomas Aquinas

He shows the effect that follows from this in the hearts of others when he then says, "On his day," which is the day of his ruin, "the youngest men will be astonished," i.e. the youngest members of the people will be stunned with great wonder, not able comprehend how such great glory of a sinner has suddenly been reduced to nothing. As for the elders he then says, "horror will invade the first men," fearing that the same thing might happen to them. …

Commentary on Job ↗