A dreadful sound is in his ears: in prosperity the destroyer shall come upon him.

Wesley's Notes

15:21 A sound - Even when he feels no evil, he is tormented with perpetual fears. Come upon him - Suddenly and unexpectedly.

King James Translators' Notes

A dreadful...: Heb. A sound of fears

Jamieson-Fausset-Brown Bible Commentary

21. An evil conscience conceives alarm at every sudden sound, though it be in a time of peace ("prosperity"), when there is no real danger (Le 26:36; Pr 28:1; 2Ki 7:6).

Matthew Henry's Concise Commentary

15:17-35 Eliphaz maintains that the wicked are certainly miserable: whence he would infer, that the miserable are certainly wicked, and therefore Job was so. But because many of God's people have prospered in this world, it does not therefore follow that those who are crossed and made poor, as Job, are not God's people. Eliphaz shows also that wicked people, particularly oppressors, are subject to continual terror, live very uncomfortably, and perish very miserably. Will the prosperity of presumptuous sinners end miserably as here described? Then let the mischiefs which befal others, be our warnings. Though no chastening for the present seemeth to be joyous, but grievous, nevertheless, afterward it yieldeth the peaceable fruits of righteousness to them that are exercised thereby. No calamity, no trouble, however heavy, however severe, can rob a follower of the Lord of his favour. What shall separate him from the love of Christ?