Charles H. Spurgeon on Psalms 121:6

The sun shall not smite thee. hrh of the sun signifies to smite injuriously (Isa 49:10), plants, so that they wither (Ps 102:5), and the head (Joh 4:8), so that symptoms of sunstroke (2Ki 4:19; Jud 8:2 seq.) appear. The transferring of the word to the word is not zeugmatic. Even the moon's rays may become insupportable, may affect the eyes injuriously, and (more particularly in the equatorial regions) produce fatal inflammation of the brain. From the hurtful influences of nature that are round about him the promise extends in verses 7,8 in every direction. Jahve, says the poet to himself, will keep (guard) thee against all evil, of whatever kind it may be and whencesoever it may threaten; he will keep thy soul, and therefore thy life both inwardly and outwardly; he will keep thy going out and coming in, i.e., all thy business and intercourse of life... everywhere and at all times; and that from this time forth even for ever. —Franz Delitzsch.