What does Psalm 134:1 mean?

Under the old covenant system, the tribe of Levi was responsible for maintaining the "house of the LORD." This "house" began as the tabernacle (Numbers 1:50) and eventually became the temple in Jerusalem (1 Kings 6:1). These areas were under perpetual watch (Leviticus 8:35). Priests were also from the tribe of Levi (Exodus 28:1; 40:13–15; Numbers 26:59). The psalmist is calling on these appointed watchmen to offer praise to the Lord even at night.

Just as God called the tribe of Levi to service, and the sons of Aaron to priesthood, He calls believers to various roles in life. The apostle Paul understood this calling on his life (1 Corinthians 1:1). He identified himself as a servant or "slave" to the Lord (Philippians 1:1). Believers may be chosen for different tasks (1 Corinthians 12:12–13), but all are important as the church serves God in the world (1 Corinthians 12:14–20).