Charles H. Spurgeon on Psalms 134:1

Behold. The first word in this verse, "Behold", seemeth to point at the reasons which the priests in the Temple had to bless Jehovah; as if it had been said, Behold, the house of God is built, the holy services are appointed, and the Lord hath given you rest from your enemies, that you may serve him acceptably; set about it, therefore, with gratitude and alacrity. We read (1Ch 9:33) that the Levitical singers were "employed in their work day and night"; to the end, doubtless, that the earthly sanctuary might bear some resemblance to that above, where St. John tells us, the redeemed "are before the throne of God, and serve him day and night in his temple": Re 7:15. —George Horne.