What does Psalm 134:3 mean?

Prior verses (Psalm 134:1–2) encouraged priests and Levites working in the temple (Leviticus 8:35) to worship God at all times. Here, the psalmist prays a blessing on those servants. He refers to God as the Creator of all things. The expression "heaven and earth" is meant to imply all of creation (Genesis 14:19; Acts 17:24). Zion is another name for the city of Jerusalem (2 Samuel 5:7; 1 Kings 8:1).

Prayers for blessing are common in the Old Testament (Psalm 128:5). One of the most common and important is the Aaronic blessing of Numbers 6:24–26:

The LORD bless you and keep you;

the LORD make his face to shine upon you and be gracious to you;

the LORD lift up his countenance upon you and give you peace.