Charles H. Spurgeon on Psalms 121:5

Shade. The Hebrew word is tsel, "a shadow, "and hence it has been supposed that the words, "thy shadow at thy right hand, "are a figurative expression, referring to the protection afforded by the shade of a tree against the scorching rays of the sun, or to the custom which prevails in tropical climates especially, of keeping off the intense heat of the sun by a portable screen, such as an umbrella or parasol. The word is often put for defence in general. Compare Nu 14:9; Isa 30:2; Jer 48:45. —James Anderson.

Verses 5-8. How large a writ or patent of protection is granted here! No time shall be hurtful, neither "day nor night, "which includes all times. Nothing shall hurt, neither sun nor moon, nor heat nor cold. These should include all annoyances. Nothing shall be hurt. "Thy soul shall be preserved, thy outgoings and thy comings in shall be preserved." These include the whole person of man, and him in all his just affairs and actions. Nothing of man is safe without a guard, and nothing of man can be unsafe which is thus guarded. They should be kept who can say, "The Lord is our keeper"; and they cannot be kept, no, not by legions of angels, who have not the Lord for their keeper. None can keep us but he, and he hath promised to keep us "for evermore." —Joseph Caryl.