Psalms 121:6

“The sun shall not smite thee by day - The Septuagint renders this, “shall not burn thee” - συγκαύσει sungkausei. So the Latin Vulgate. The Hebrew word means to smite, to strike, as with a rod or staff, or with the plague or pestilence; and then, to kill, to slay. The allusion here is to what is now called a “sun-stroke” - the effect of the burning sun on the brain. Such effects of the sun are often fatal now, as doubtless they were in the time of the psalmist. Nor the moon by night - The psalmist here refers to some prevalent opinion about the influence of the moon, as endangering life or health. Some have supposed that he refers to the sudden cold which follows the intense heat of the day…”

“Smite - With excessive heat. Moon - With that cold and moisture which come into the air by it. Intemperate heats and colds are the springs of many diseases. Next: Psalms Chapter 122”

“the sun: Psa 91:5-10; Isa 49:10; Rev 7:16 Psalms 121:7”