Charles H. Spurgeon on Psalms 121:3

He will not suffer thy foot to be moved. A man cannot go without moving of his feet; and a man cannot stand whose feet are moved. The foot by a synechdoche is put for the whole body, and the body for the whole outward estate; so that, "He will not suffer thy foot to be moved", is, he will not suffer thee or thine to be moved or violently cast down. The power of thine opposers shall not prevail over thee, for the power of God sustains thee. Many are striking at thy heels, but they cannot strike them up while God holds thee up. If the will of thine enemies might stand, thou shouldest quickly fall; but God "will not suffer thy foot to be moved". —Joseph Caryl.

Verses 3-8. There is something very striking in the assurance that the Lord with not suffer the foot even of the most faint and wearied one to be moved. The everlasting mountains stand fast, and we feel as if, like Mount Zion, they could not be removed for ever; but the step of man —how feeble in itself, how liable to stumble or trip even against a pebble in the way! Yet that foot is as firm and immoveable in God's protection as the hills themselves. It is one of his own sweet promises, that he will give his angels charge over every child Of his, that lie come to no harm by the way. But, oh, how immeasurably beyond even the untiring wings of angels is the love promised here! that love which engages to protect from every danger, as a hen gathereth her chickens under her wings. In the hours of occupation and hurry, in the conflicts and perils of the day, in the helplessness of sleep, in the glare and heat of the noonday, amid the damps and dews of night, that wakeful eye is still over every child for his good. Man, indeed, goeth forth to his work and to his labour till the evening; but alike as he goes forth in the morning, and as he returns in the evening, the Lord still holds him up in all his goings forth and his comings in; no manner of evil shall befall him. And oh! what a sweet addition is it to the promise, "He shall preserve thy soul". It is the very argument of the apostle, and the very inference he draws, "The eyes of the Lord are upon the righteous, and his ears are open unto their cry", —"He neither slumbereth nor sleepeth", —and then he asks, "Who is he that will harm you, if ye be followers of that which is good?" From the very dawn of life to its latest close, even for evermore, "He will preserve thee from all evil; he will preserve thy soul." —Barton Bouchier.

Verses 3, 4, 5. A great practical difficulty is to find a keeper who will remain awake during the whole night. The weariness of those who keen a faithful watch, and their longing for day during the tedious lonely hours of darkness, is alluded to in a graphic and beautiful figure of the Psalmist —

"My soul waiteth for the Lord

More than keepers for the morning,

More than keepers for the morning."

The usual method adopted to secure due vigilance is to require the man to call out loudly, or to blow a whistle, every quarter of an hour... Yet, notwithstanding all precautions, as soon as sleep falls on the tired camp, it is too often the case that the hireling keeper lies down on the ground, wraps around him his thick "abaiyeh", or cloak, and, careless of his charge, or overcome with weariness yields himself up to his drowsy propensities. Viewed in the light of these facts, how full of condescension and cheer is the assurance of God's never ceasing care —

"He who keepeth thee will not slumber.

Behold, he who keepeth Israel

Doth not slumber or sleep.

Jehovah is thy keeper."

While the services of the keeper constitute at all times a marked feature of life in Palestine, they are perhaps more needed when travelling through the country than at any other time. Then, when the moving camp is nightly pitched in strange fields, it becomes absolutely necessary to apply to the nearest authorities for a nocturnal guardian, before one can safely lie down to rest. Now this Psalm 121 being one of "the Songs of Degrees, "was probably composed to be sung on the way to Jerusalem, as a pilgrim hymn, when the Israelites were coming up annually to keep the three great feasts. As a journeying psalm, it would therefore have peculiar significance in its allusion to the keeper by night. —James Neil, in "Palestine Explored," 1882.