Albert Barnes Commentary Job 31:3

"Is it not calamity to the unrighteous, And disaster to the workers of iniquity?" — Job 31:3 (ASV)

Is not destruction to the wicked? — That is, Job says that he was well aware that destruction would overtake the wicked, and that if he had given indulgence to impure desires, he could have expected nothing else. Well knowing this, he says, he had guarded himself in the most careful manner from sin and had labored with the greatest diligence to keep his eyes and his heart pure.

And a strange punishment — ונכר wəneker. The word used here means literally strangeness—a strange thing, something with which we were unfamiliar. It is used here evidently in the sense of a strange or unusual punishment, something that does not occur in the ordinary course of events. The sense is that for the sin particularly referred to here, God would intervene to inflict vengeance in a manner that did not occur in the ordinary dealings of his providence. There would be some punishment specially chosen for this sin, which would mark it with his special displeasure.

Has it not been so in all ages? The Vulgate renders it alienatio, and the Septuagint translates it in a similar manner—ἀπαλλοτρίωσις apallotriōsis—and they seem to have understood it as followed by entire alienation from God, an idea that would be everywhere sustained by a reference to the history of the sin referred to by Job.

There is no sin that so greatly poisons all the fountains of pure feeling in the soul, and none that will so certainly terminate in the entire wreck of character.