At his day, i.e. at the day of his destruction, as the word day is used, Psalms 37:13, Psalms 137:7 Ezekiel 21:25 Obadiah 1:12. They shall be amazed at the suddenness, and dreadfulness, and prodigiousness of it, as Job's friends were at his calamities, Job 2:12,13. They that went before, i.e. before the persons last mentioned; those who lived in the time and place where this judgment was inflicted. Affrighted; or, filled with horror; partly through humanity and compassion, and partly for fear, lest the judgment should overtake them also.
Related Commentaries of Job 18:20
Job 18:20
20 They that come after him shall be astonied at his day, as they that went before were affrighted.