Albert Barnes 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)

Behold - As if calling attention to the fact that they were there, or had come.

Bless you the Lord - Praise Yahweh. This call expresses their desire that God should be praised and calls on those who presided over the public worship of the sanctuary to engage now in that service as expressive of their feelings.

All you servants of the Lord - The priests or ministers of religion, appointed especially to this service.

Which by night stand in the house of the Lord - This refers to a class of singers in the temple who devoted the night, or a part of the night, to praise; and it is possible that this service, as it was subsequently in some monasteries, was continued by succeeding choirs throughout the entire night. Thus, in 1 Chronicles 9:33, it is said, And these are the singers, chief of the fathers of the Levites, who remaining in the chambers were free, for they were employed in that work day and night.

This class is particularly addressed in this psalm, as if they were especially favored, or as if they especially possessed the ear of God in the silence of the night when the world slumbered around them.

There is something favorable to devotion in the silence of the night: when the world sleeps, when we are alone with God, and when it seems as if God would more particularly attend to our cry, since the rest of the world is still and, as it were, does not need His care.

All this may be fancy; but the effect may be to make the mind more solemn, and better suited for devotion.