This psalm is entitled simply, "A Song of Degrees." See the notes on the title to Psalm 120:1-7. Nothing is known, or can be known, of the author or of the occasion on which it was composed. DeWette and Rosenmuller suppose that it was composed in the exile; Rosenmuller regarding it as a psalm to be sung on the return to Palestine after the captivity - DeWette, as the psalm of a pensive exile looking toward the hills of Palestine, his native land, as the source from where all his help must come - and expressing confidence in God that he would bring him out of his exile and his trouble. There is no proof, however, that either of these suppositions is correct. The language is such, indeed, as might then be employed, but it is also such as might be used on many other occasions. It might be the language of the leader of an army, endangered, and looking to the "hills" where he expected reinforcements; it might be that of a pious man encompassed with dangers, anal using this expression as illustrative of his looking up to God; or it might be the language of one looking directly to heaven, represented as the heights, or the exalted place where God dwells; or it might be the language of one looking to the hills of Jerusalem - the seat of the worship of God - the place of His abode - as his refuge, and as the place from where only help could come. This last seems to me to be the most probable supposition; and thus the psalm represents the confidence and hope of a pious man (in respect to duty, danger, or trial) as derived from the God whom he worships - and the place where God has fixed his abode - the church where he manifests himself to people.

The resolution of a godly man, Psalm 121:1, Psalm 121:2. The safety and prosperity of such, as they and theirs shall be under the continual protection of God, Psalm 121:3-8.
This appears to be a prayer of the Jews in their captivity, who are solicitous for their restoration. It is in the form of a dialogue.
Psalm 121:1, Psalm 121:2. The person who worships God speaks the two first verses, "I will lift up mine eyes-my help cometh," - Psalm 121:1, Psalm 121:2.
Psalm 121:3. The ministering priest answers him, "He will not suffer thy foot to be moved." "He that keepeth thee will not slumber," Psalm 121:3.
To which the worshipper answers, that he knows that "he who keepeth Israel shall neither slumber nor sleep," Psalm 121:4; but he seems to express a doubt whether he shall be an object of the Divine attention.
Psalm 121:5 etc. The priest resumes; and, to the conclusion of the Psalm, gives him the most positive assurances of God's favor and protection.

INTRODUCTION TO PSALM 121
A Song of degrees. The inscription of the Syriac version is,
"one of the songs of ascent out of Babylon.''
Aben Ezra thinks it was composed on account of Israel, when in a siege and distress; or, adds he, on account of the children of our captivity; the present state of the Jews. Grotius is of opinion it was written by David, at the time of the battle with Absalom. Some take it to be a military psalm, proper for soldiers engaged with an enemy: others, that it is suitable for travellers when on a journey; and why not for persons also, when they commit themselves to God in the night watches, and about to take rest? And indeed it is suitable at all times; when the good man may, with the psalmist, expect divine help, and be secure of protection and preservation.

The safety of the godly.

The Consolation of Divine Protection
This song of degrees is the only one that is inscribed שׁיר למעלות and not שׁיר המעלות. The lxx, Targum, and Jerome render it as in the other instances; Aquila and Symmachus, on the contrary, ᾠδὴ (ᾆσμα) εἰς τάς ἀναβάσεις, as the Midrash Sifrı̂ also mystically interprets it: Song upon the steps, upon which God leads the righteous up into the other world. Those who explain המעלות of the homeward caravans or of the pilgrimages rightly regard this למעלות, occurring only once, as favouring their explanation. But the Lamed is that of the rule or standard. The most prominent distinguishing mark of Psalm 121:1-8 is the step-like movement of the thoughts: it is formed למּעלות, after the manner of steps. The view that we have a pilgrim song before us is opposed by the beginning, which leads one to infer a firmly limited range of vision, and therefore a fixed place of abode and far removed from his native mountains. The tetrastichic arrangement of the Psalm is unmistakeable.