By night, when evil accidents are most terrible and least avoidable. The arrow; the pestilence, or any such common and destructive calamity; for such are frequently called God's arrows, as Dent. Deuteronomy 32:23,42 La 3:12,13, &c. By day, which is the time for shooting of arrows. The sense of the verse is, He shall be kept from secret and open mischiefs at all times.
Related Commentaries of Psalms 91:5
Psalms 91:5
5 Thou shalt not be afraid for the terror by night; nor for the arrow that flieth by day;