will not harm you
The phrase speaks to God's protective nature. The Hebrew word for harm, "נָכָה" (nakah), can mean to strike or smite. This assurance is a promise that God will shield His people from the destructive forces that could otherwise overwhelm them. In a broader biblical context, this protection is not just physical but also spiritual, as God guards the hearts and minds of His followers. This promise is echoed in other scriptures, such as Isaiah 54:17, which assures that no weapon formed against God's people will prosper.

by day
This phrase emphasizes the continual nature of God's protection. The day, with its activities and potential hazards, is a time when one might be most vulnerable to external threats. The assurance that God protects "by day" is a reminder that His vigilance is unceasing. In the biblical narrative, daytime is often associated with work and activity, as seen in John 9:4, where Jesus speaks of doing the works of God while it is day. Thus, this protection extends to all aspects of daily life and endeavors.

nor the moon
The moon, "יָרֵחַ" (yareach) in Hebrew, governs the night and is often associated with the mysterious and unknown. In ancient times, the night was a time of fear and uncertainty, with dangers lurking in the darkness. The moon's mention here signifies that God's protection is not limited to the day but extends into the night. This reflects the comprehensive nature of God's care, as seen in Psalm 139:12, where even the darkness is not dark to God.

by night
The night, with its inherent uncertainties and fears, is a time when one might feel most vulnerable. The assurance that God protects "by night" is a powerful reminder of His omnipresence and omnipotence. In biblical times, night was often associated with danger and evil, as seen in the parable of the wheat and tares in Matthew 13:25, where the enemy sows weeds at night. Yet, God's promise here is that His protection is as steadfast in the night as it is in the day, offering peace and security to His people at all times.

Nor the moon by night.--Possibly there is allusion to the belief, so common in old times, of the harmful influence of the moon's light--a belief still recalled in the word lunacy. It is a fact that temporary blindness is often caused by moonlight. (See authorities referred to by Ewald and Delitzsch.) Others, again, think that the injurious cold of the night is here placed in antithesis to the heat of the noonday sun (comp. Genesis 31:40; Jeremiah 36:30), the impression that intense cold burns being common in the East, as indeed everywhere. Tennyson speaks of the moon being "keen with frost." But it is also possible that the generally harmful effects of night air are intended. . . .