This is the last psalm of the collection or group called "Songs of Degrees," and it is of the nature of a doxology as now sung in our places of worship. Its author is unknown. From anything that appears in the psalm itself, it may have been composed originally to occupy the very place which it does occupy here. The psalm is a summons to praise, and it would seem not improbable that it was designed to be sung by alternate choirs - the first Psalm 134:1-2 representing the people approaching the sanctuary, calling on those who habitually serve God there - the ministers of religion - to lift up their hands in the sanctuary and to praise the Lord; the second Psalm 134:3, the response of the priests or the ministers of religion, pronouncing a blessing on the people - a blessing as proceeding out of Zion.

An exhortation to praise God in his sanctuary, Psalm 134:1-3.
This is the last of the fifteen Psalm called Psalm of degrees. Who was the author is uncertain; it is attributed to David only by the Syriac; it is intimately connected with the two preceding Psalm, and is an exhortation to the priests and Levites who kept nightly watch in the temple, to the assiduous in praising the Lord. It seems to consist of two parts: 1. An exhortation, probably from the high priest, to those priests and Levites who kept watch in the temple by night, to spend their time profitably, and duly celebrate the praises of God, Psalm 134:1, Psalm 134:2. The second part, which is contained in the Psalm 134:3, is the prayer of the priests and Levites for the high priest, who seems now to be going to his rest.

INTRODUCTION TO PSALM 134
A Song of degrees. This is the last of the psalms called "songs of degrees"; of which See Gill on Psalm 120:1, title. It is thought to be written by David, either when he brought the ark to Zion, 2-Samuel 6:17; or rather when he numbered the Levites, and appointed them their service, 1-Chronicles 23:26. So the Syriac inscription,
""a psalm" of David, concerning the priests, whom he appointed to wait on the ministry of the Lord in the nights; but, spiritually, an instruction of life.''
Aben Ezra connects it with the preceding psalm,
"as the dew of Hermon ye shall be that bless; behold, therefore, ye are bound to bless the Lord?''.

An exhortation to bless the Lord.

Night-Watch Greeting and Counter-Greeting
This Psalm consists of a greeting, Psalm 134:1-2, and the reply thereto. The greeting is addressed to those priests and Levites who have the night-watch in the Temple; and this antiphon is purposely placed at the end of the collection of Songs of degrees in order to take the place of a final beracha. In this sense Luther styles this Psalm epiphonema superiorum. It is also in other respects (vid., Symbolae, p. 66) an appropriate finale.