Adam Clarke on Psalms 121

Unto the hills - Jerusalem was built upon a mountain; and Judea was a mountainous country; and the Jews, in their several dispersions, turned towards Jerusalem when they offered up their prayers to God.

My help cometh from the Lord - There is no help for me but in my God; and I expect it from no other quarter.

He will not suffer thy foot to be moved - The foundation, God's infinite power and goodness, on which thou standest, cannot be moved; and whilst thou standest on this basis, thy foot cannot be moved.

He that keepeth Israel - The Divine Being represents himself as a watchman, who takes care of the city and its inhabitants during the night-watches; and who is never overtaken with slumbering or sleepiness. There is a thought in the Antigone of Sophocles, that seems the counterpart of this of the psalmist, Ταν σαν, Ζευ, δυναμιν τις ανδρων Ὑπερβασια κατασχοι, Ταν ουθ' ὑπνος αἱ - ρει ποθ' ὁ παντογηρως, Ακαματοι τε θεων Μηνες;

Antig. ver. 613, Edit. Johnson.

Shall men below control great Jove above,Whose eyes by all-subduing sleep

Are never closed, as feeble mortals' are;But still their watchful vigil keep

Through the long circle of th' eternal year?

Franklin.

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.

The Lord shall preserve thee from all evil - Spiritual and corporeal, natural and moral.

He shall preserve thy soul - Take care of thy life, and take care of thy soul.

Thy going out and thy coming in - Night and day - in all thy business and undertakings; and this through the whole course of thy life: for evermore.