The sun shall not smite thee by day, nor the moon by night. The sun shall not smite thee by day - Thus expressed by the Chaldee: "The morning spectres shall not smite thee by day, during the government of the sun; nor the nocturnal spectres by night, during the government of the moon." I believe the psalmist simply means, they shall not be injured by heat nor cold; by a sun-stroke by day, nor a frost-bite by night.
Related Commentaries of Psalms 121:6
Psalms 121:6
6 The sun shall not smite thee by day, nor the moon by night.