John Gill Commentary Psalms 91:8

"Only with thine eyes shalt thou behold, And see the reward of the wicked." — Psalms 91:8 (ASV)

Only with your eyes you shall behold
The flying arrow, the walking pestilence, and wasting destruction, and the great devastations made by it:

and see the reward of the wicked ;
the vengeance of God upon them, and this as a just punishment for their sins; not looking upon it with delight and pleasure, rejoicing in the misery of their fellow creatures, any otherwise than as the glory of divine justice is displayed in it; see (Psalms 52:6) (68:10) , the pestilence is always threatened, and it always comes, as a Judgment upon a wicked generation of men; and so it is ever to be considered, and is considered by good men, (Leviticus 26:5) (Deuteronomy 28:20Deuteronomy 28:21) .