Charles Ellicott Commentary Psalms 134:1

"Behold, bless ye Jehovah, all ye servants of Jehovah, That by night stand in the house of Jehovah." — Psalms 134:1 (ASV)

All you servants: We learn from 1 Chronicles 9:33 that there were Levites whose duties brought them to the Temple by night. Moreover, the word ‘âmad, “stand,” is the customary word for sacerdotal service (Deuteronomy 10:8; Deuteronomy 18:7; 1 Chronicles 23:30, etc.).