Matthew Poole and continuators on Psalms 121:6

6 The sun shall not smite thee by day, nor the moon by night.

With excessive heat.

With that cold and moisture which comes into the air by it and with it. Intemperate heats and colds are the two springs of many diseases. He alludes both to the condition of Souldiers or Travellers, who are exposed to the open air by day and by night, and also to the cloudy Pillar which defended the Israelites both by day and by night. The sence is, He shall protect thee from all evils both by day and night.