Albert Barnes Commentary Psalms 121:5

"Jehovah is thy keeper: Jehovah is thy shade upon thy right hand." — Psalms 121:5 (ASV)

The Lord is thy keeper - Your Preserver; your Defender. He will keep you from danger; He will keep you from sin; He will keep you unto salvation.

The Lord is thy shade - The Lord is as a shadow: as the shadow of a rock, a house, or a tree, in the intense rays of the burning sun. See the notes at Isaiah 25:4.

Upon thy right hand - See Psalms 16:8; Psalms 109:31. Perhaps the particular allusion to the right hand here may be that that was the place of a protector. He would thus be at hand, or would be ready to interpose in defense of him whom He was to guard. It is possible, however, that the idea here may be derived from the fact that in Scripture the geographer is represented as looking to the east, and not toward the north, as with us. Hence, the south is always spoken of as the right, or at the right hand (compare the notes at Psalms 89:12); and as the intense rays of the sun are from the south, the idea may be, that God would be as a shade in the direction from which those burning rays came.