Synopsis of the Books of the Bible, by John Nelson Darby, [1857-62], at sacred-texts.com
Psalms Chapter 121
In Psalm 121 Jehovah is assuredly declared to be his protection. He who never slumbers nor sleeps He will not suffer his foot to be moved. The general intention is plain. I am not quite sure what is the force of Verse 1, (Psa 121:1), unless to identify Jehovah, the Creator of heaven and earth, with the hill of Zion, [See Note #1] and the city of the great King. However this may be, Jehovah (as the great security) is the subject of the psalm. This is very distinct, and His name reiterated for the purpose. He is referred to in the double character, Creator of heaven and earth, and the Keeper of Israel, especially of the godly: Jehovah would preserve him in all circumstances and for ever.
Note #1
A hill is used as a symbol of exalted strength, a high hill as the hill of Bashan. This is the Lord's hill.