Albert Barnes Commentary Job 21:9

"Their houses are safe from fear, Neither is the rod of God upon them." — Job 21:9 (ASV)

Their houses are safe from fear - Margin, “peace from.” The friends of Job had maintained just the contrary; see (Job 20:27–28); (Job 15:21–24). Their idea was that the wicked man would never be free from alarms. Job says that they lived in security and peace, and that their houses are preserved from the intrusions of evil-minded people.

Neither is the rod of God upon them - The “rod” is an emblem of punishment. The idea is that they were free from the chastisements which their sins deserved. There can be no doubt that there are enough cases in which the wicked live in security, to justify Job in all that he affirms here, as there are enough instances in which the wicked are cut off for their sins to make what his friends said plausible. The truth is, good and evil are intermingled.

There is a “general” course of events by which the wicked are involved in calamity in this life, and the righteous are prospered; but still, there are so many exceptions as to show the necessity of a future state of rewards and punishments. To us, who look to that future world, all is clear. But that view of the future state of retribution was not possessed by Job and his friends.