Explanatory Notes on the Whole Bible, by John Wesley, [1754-65], at sacred-texts.com
psa 134:1Servant - Peculiarly so called, priests and Levites. Night - Not only by day, but also by night, when their watch was more necessary. Stand - Serve or minister.
psa 134:3Thee - Thee whosoever thou art who dost faithfully perform the duty here commanded.