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1 I will lift up mine eyes unto the hills, from whence cometh my help. 2 My help cometh from the LORD, which made heaven and earth. 3 He will not suffer thy foot to be moved: he that keepeth thee will not slumber. 4 Behold, he that keepeth Israel shall neither slumber nor sleep. 5 The LORD is thy keeper: the LORD is thy shade upon thy right hand. 6 The sun shall not smite thee by day, nor the moon by night. 7 The LORD shall preserve thee from all evil: he shall preserve thy soul. 8 The LORD shall preserve thy going out and thy coming in from this time forth, and even for evermore.
[AD 430] Augustine of Hippo on Psalms 121:1
...Let them "lift up their eyes to the hills whence comes their help" [Psalm 121:1]. What means, The hills have been lightened? The San of righteousness has already risen, the Gospel has been already preached by the Apostles, the Scriptures have been preached, all the mysteries have been laid open, the veil has been rent, the secret place of the temple has been revealed: let them now at length lift their eyes up to the hills, whence their help comes..."Of His fullness have all we received," [John 1:16] he says. Your help therefore is from Him, of whose fullness the hills received, not from the hills; towards which, nevertheless, save thou lift your eyes through the Scriptures, you will not approach, so as to be lighted by Him.

[AD 430] Augustine of Hippo on Psalms 121:1-2
And say, “I have lifted my eyes to the mountains from which help shall come to me” in such a way that you add to it immediately, “My help is from the Lord, who made heaven and earth.” Therefore let us lift our eyes to the mountains from which help shall come to us. Yet it is not the mountains themselves in which our hope is to be placed, for the mountains receive what they may present to us. Therefore we must put our hope in that place from which the mountains also receive [what they give to us]. When we lift our eyes to the Scriptures, because the Scriptures were delivered through people, we lift our eyes to the mountains from which help will come to us; and yet since they who wrote the Scriptures were themselves people, they were not providing enlightenment from themselves. Rather, Christ was the true light who enlightens everyone coming into the world.

[AD 430] Augustine of Hippo on Psalms 121:1-2
However just people may be, however preeminent in grace, however luminous their wisdom, however great the merits that set them on a pinnacle, they are only mountains. Pay attention to the psalm: “I lifted up my eyes to the mountains, from where my help shall come,” because “there was a man sent by God, whose name was John; this man came to bear witness to the light.” So you have lifted up your eyes to the mountain John, from where your help may come, because he is bearing witness to the light. Continue with the psalm; do not stop on the mountain: “My help is from the Lord, who made heaven and earth.” That is Christ; “all things were made through him.” He is the constructor of the world; he is, you see, the Word of the Father; the Father made all things through the Word.

[AD 430] Augustine of Hippo on Psalms 121:1-2
The Son of God, the only begotten of the Father, God always, man for our sake, having become what he made—I mean, he became man, having made humankind—says to the Father, “I confess to you, Father, Lord of heaven and earth.” “You are my Father, Lord of heaven and earth”; Father of the one through whom all things were made. The whole of creation, you see, is briefly unfolded in these two words, heaven and earth. That is why it says in the first book of God’s Scriptures, “In the beginning, God made heaven and earth”12; and also, “My help is from the Lord, who made heaven and earth.” But by the word heaven is to be understood whatever is in the heavens, and by the word earth whatever is on the earth; so by naming these two parts of creation, you do not leave out a single creature, because it is either here, or it is there.

[AD 585] Cassiodorus on Psalms 121:1-2
When he says, “I lifted up,” he shows that he had advanced to a certain contemplation. Lifting up is bringing something to higher levels. “My eyes” refers to the sight of the heart. The following has been written about them: “Unveil my eyes and I will consider marvelous things from your law” and “The commandment of the Lord is clear, illuminating the eyes.” If you were to turn those eyes of flesh, what good would it have been if he had chosen to see mountains situated among forests or rough rocks? But if you were to investigate this matter spiritually, it is altogether beneficial that he be believed to have lifted the eyes of his heart either to holy men or to the divine books or to lofty angels. They are truly mountains in their size and solidity. If he sought help from them, he was sustained. But lest we should perhaps put our hope in the mountains previously spoken about, the second verse shows whence truly our help can come: the one arranging all things in a salutary order. Thus, insofar as there is hope in the mountains, it is nonetheless so that we may know that the Lord offers help to us through them. It is the Lord from whom are the needed kindness and salvific protection and unshaken happiness, as the apostle says: “Neither is he who plants anything nor he who waters, but God who gives the growth.” And lest you might think that there is another Lord, since this word is equivocable, he says, “[the Lord] who made heaven and earth,” meaning the Word, through whom all things were made.

[AD 430] Augustine of Hippo on Psalms 121:3
Sing therefore what follows; if you wish to hear how you may most securely set your feet on the steps, so that you may not be fatigued in that ascent, nor stumble and fall: pray in these words: "Suffer not my foot to be moved!" [Psalm 121:3]. Whereby are feet moved; whereby was the foot of him who was in Paradise moved? But first consider whereby the feet of him who was among the Angels were moved: who when his feet were moved fell, and from an Angel became a devil: for when his feet were moved he fell. Seek whereby he fell: he fell through pride. Nothing then moves the feet, save pride: nothing moves the feet to a fall, save pride. Charity moves them to walk and to improve and to ascend; pride moves them to fall...Rightly therefore the Psalmist, hearing how he may ascend and may not fall, prays unto God that he may profit from the vale of misery, and may not fail in the swelling of pride, in these words, "Suffer not my feet to be moved!" And He replies unto him, "Let him that keeps you not sleep." Attend, my beloved. It is as if one thought were expressed in two sentences; the man while ascending and singing "the song of degrees," says, "Suffer not my foot to be moved:" and it is as if God answered, You say unto Me, Let not my feet be moved: say also, "Let Him that keeps you not sleep," and your foot shall not be moved.

[AD 379] Basil of Caesarea on Psalms 121:4
We attribute to God, as it were, every state that corresponds to our circumstances. For this reason, when we are half asleep and behaving slothfully, God, since he judges us unworthy of his observant watchfulness over us, is said to be asleep. But, when, after noticing at some time the harm that comes from his sleeping, we shall say, “Arise, why do you sleep, O Lord?” “Behold, he shall neither slumber nor sleep at that time, that keeps Israel.” Some others, as it were, turn their eyes away from God because of their shameful deeds and their acts unworthy of the eyes of God. These, on repenting, say, “Why do you turn your face away?” Besides these, there are others who have cast out the memory of God and, as it were, are producing in him forgetfulness of themselves, and these say, “Why do you forget our want and our trouble?” In a word, people do the very things that are humanly spoken about God, making God behave in ways appropriate to the manner in which they have been made. Therefore, “I will extol you, O Lord, for you have upheld me; and you have not made my enemies to rejoice over me.” And I will suffer nothing low or abject in my life.

[AD 420] Jerome on Psalms 121:4
[Daniel 4:13-14] "'And behold, a watchman and a holy one descended from heaven, and he cried out with a loud voice and spoke as follows: 'Cut down the tree and chop off its branches...'" Instead of "watchman" Theodotion uses the Chaldee word itself, hir, which is written with the three letters 'ayin, yodh, and resh. But it signifies the angels, because they ever keep watch and are prepared to carry out God's command. And so we too follow the example of the angels in their duties when we engage in frequent night-long vigils. Also it is said of the Lord: "He who keepeth Israel will neither slumber nor sleep" (Psalm 121:4). Lastly, we read a little later:

[AD 430] Augustine of Hippo on Psalms 121:4
Choose for yourself Him, who will neither sleep nor slumber, and your foot shall not be moved. God is never asleep: if you dost wish to have a keeper who never sleeps, choose God for your keeper. "Suffer not my feet to be moved," you say, well, very well: but He also says unto you, "Let not him that keeps you slumber." Thou perhaps wast about to turn yourself unto men as your keepers, and to say, whom shall I find who will not sleep? What man will not slumber? Whom do I find? Whither shall I go? Whither shall I return? The Psalmist tells you: "He that keeps Israel, shall neither slumber nor sleep" [Psalm 121:4]. Do you wish to have a keeper who neither slumbers nor sleeps? Behold, "He that keeps Israel shall neither slumber nor sleep:" for Christ keeps Israel. Be thou then Israel. What means Israel? It is interpreted, Seeing God. And how is God seen? First by faith: afterwards by sight. If you can not as yet see Him by sight, see Him by faith...Who is there, who will neither slumber nor sleep? When you seek among men, you are deceived; you will never find one. Trust not then in any man: every man slumbers, and will sleep. When does he slumber? When he bears the flesh of weakness. When will he sleep? When he is dead. Trust not then in man. A mortal may slumber, he sleeps in death. Seek not a keeper among men.

[AD 430] Augustine of Hippo on Psalms 121:4
Not without reason, brothers. For Samaritan is interpreted as guard. He knew that he was our guard. For “he neither slumbers nor sleeps, who guards Israel,” and “Unless the Lord guard the city, in vain do they who guard watch.” He who is our Creator is our guard. For did it suit him that we be redeemed but not that we be saved?

[AD 458] Theodoret of Cyrus on Psalms 121:4
Regarding the divine nature the prophet David says, “Behold, he who keeps Israel shall neither slumber nor sleep.” But the narrative of the Evangelist describes the Master Christ as sleeping in the boat. Now not sleeping and being asleep are two contrary ideas, so the prophet contradicts the Gospels if, as they argue, the Master Christ was God alone. There is no contradiction, for both prophecies and Gospels flow from one and the same spirit. The Master Christ therefore had a body, akin to all other bodies, affected by the need of sleep. So the argument for the confusion is proved a fable.Regarding the divine nature the prophet Isaiah said, “He shall neither be hungry nor weary” and so on. But the Evangelist says, “Jesus, being weary with his journey, sat thus by the well”;23 and “shall not be weary” is contrary to “being weary.” Therefore the prophecy is contrary to the narrative of the Gospels. But they are not contrary, for both are descriptive of one God. Not being weary is proper to the uncircumscribed nature that fills all things. But moving from place to place is proper to the circumscribed nature. When that which moves is constrained to travel, it is subject to the weariness of the wayfarer. Therefore what walked and was weary was a body, for the union did not confound the natures.

[AD 430] Augustine of Hippo on Psalms 121:5
Let us now come to this verse of the Psalm: "The Lord is your defence upon the hand of your right hand" [Psalm 121:5]. By hand he means power. How do we prove this? Because the power of God also is styled the hand of God...Whereof John says, "He gave unto them power to become the sons of God." [John 1:12] Whence have you received this power? "To them," he says, "that believe in His Name." If then you believe, this very power is given you, to be among the sons of God. But to be among the sons of God, is to belong to the right hand. Your faith therefore is the hand of your right hand: that is, the power that is given you, to be among the sons of God, is the hand of your right hand...

[AD 430] Augustine of Hippo on Psalms 121:6
"May the Lord shield you upon the hand of your right hand" [Psalm 121:6]. I have said, and I believe you have recognised it. For had ye not recognised it, and that from the Scriptures, you would not signify your understanding of it by your voices. Since then you have understood, brethren, consider what follows; wherefore the Lord shields you "upon the hand of your right hand," that is, in your faith, wherein we have received "power to become the sons of God," and to be on His right hand: wherefore should God shield us? On account of offenses. Whence come offenses? Offences are to be feared from two quarters, for there are two precepts upon which the whole Law hangs and the Prophets, the love of God and of our neighbour. [Matthew 22:37-40] The Church is loved for the sake of our neighbour, but God for the sake of God. Of God, is understood the sun figuratively: of the Church, is understood the moon figuratively. Whoever can err, so as to think otherwise of God than he ought, believing not the Father and the Son and the Holy Ghost to be of one Substance, has been deceived by the cunning of heretics, chiefly of the Arians. If he has believed anything less in the Son or in the Holy Spirit than in the Father, he has suffered an offense in God; he is scorched by the sun. Whoever again believes that the Church exists in one province only, and not that she is diffused over the whole world, and whoso believes them that say, "Lo here," and "Lo there, is Christ," [Matthew 24:23] as you but now heard when the Gospel was being read; since He who gave so great a price, purchased the whole world: he is offended, so to speak, in his neighbour, and is burnt by the moon. Whoever therefore errs in the very Substance of Truth, is burnt by the sun, and is burnt through the day; because he errs in Wisdom itself...God therefore has made one sun, which rises upon the good and the evil, that sun which the good and the evil see; but that Sun is another one, not created, not born, through whom all things were made; where is the intelligence of the Immutable Truth: of this the ungodly say, "the Sun rose not upon us." Whosoever errs not in Wisdom itself, is not burnt by the sun. Whosoever errs not in the Church, and in the Lord's Flesh, and in those things which were done for us in time, is not burnt by the moon. But every man although he believes in Christ, errs either in this or that respect, unless what is here prayed for, "The Lord is your defence upon the hand of your right hand," is realized in him. He goes on to say, "So that the sun shall not burn you by day, nor the moon by night" [Psalm 121:6]. Your defence, therefore, is upon the hand of your right hand for this reason, that the sun may not burn you by day, nor the moon by night. Understand hence, brethren, that it is spoken figuratively. For, in truth, if we think of the visible sun, it burns by day: does the moon burn by night? But what is burning? Offence. Hear the Apostle's words: "Who is weak, and I am not weak? Who is offended, and I burn not?" [2 Corinthians 11:29]

[AD 430] Augustine of Hippo on Psalms 121:7-8
"For the Lord shall preserve you from all evil" [Psalm 121:7]. From offenses in the sun, from offenses in the moon, from all evil shall He preserve you, who is your defence upon the hand of your right hand, who will not sleep nor slumber. And for what reason? Because we are amid temptations: "The Lord shall preserve you from all evil. The Lord preserve your soul:" even your very soul. "The Lord preserve your going out and your coming in, from this time forth for evermore" [Psalm 121:8]. Not your body; for the Martyrs were consumed in the body: but "the Lord preserve your soul;" for the Martyrs yielded not up their souls. The persecutors raged against Crispina, whose birthday we are today celebrating; they were raging against a rich and delicate woman: but she was strong, for the Lord was her defence upon the hand of her right hand. He was her Keeper. Is there any one in Africa, my brethren, who knows her not? For she was most illustrious, noble in birth, abounding in wealth: but all these things were in her left hand, beneath her head. An enemy advanced to strike her head, and the left hand was presented to him, which was under her head. Her head was above, the right hand embraced her from above.. ..

[AD 430] Augustine of Hippo on Psalms 121:8
“May the Lord protect your coming in and your going out.” Now look at the coming out of the furnace and the going into it; “Reckon it all joy, my brothers, when you fall into various trials.” There you are, you have heard about the entrance; now find the exit. It is easy enough to go in; coming out is the big thing. But do not worry: “God is faithful”—because you have gone in, you are naturally thinking about getting out—“God is faithful and does not allow you to be tempted above what you are able to bear, but with the temptation he will also make a way out.” What is the way out? “That you may be able to endure.” You have gone in, you have fallen in, you have endured, you have come out.