Adam Clarke on Psalms 134

Behold, bless ye the Lord - I believe הנה hinneh should be taken here in the sense of take heed! Be upon your guard; you serve a jealous God; provoke him not.

Which by night stand - Who minister during the night.

Lift up your hands in the sanctuary - קדש kodesh, "in holiness:" or, as the Syriac, lekoudishe, "to holiness;" in sancta, Vulgate; and εις τα ἁγια, Septuagint; "in holy things; or, as the Aethiopic, in the house of the sanctuary." The expression seems very similar to that of St. Paul, 1Tim 2:8 : "Lifting up holy hands, without wrath and doubting."

Bless the Lord - That is, speak good of his name: tell the wonders he has wrought, and show that his name is exalted.

The Lord that made heaven and earth - Who governs and possesses all things; and who can give you every spiritual and earthly blessing.

Bless thee out of Zion - As if they had said, "We will attend to your orders; go in peace, and may God shower down his blessings upon you!" The blessing pronounced by the priests was the following: "The Lord bless thee and keep thee! The Lord make his face shine upon thee, and he gracious unto thee! The Lord lift up his countenance upon thee, and give thee peace!" Num 6:24-26.