What does Psalm 122:9 mean?

As the psalm prays for peace over Jerusalem (Psalm 122:6–8), it now turns to concern for the temple. In David's day, the tabernacle (Exodus 25—28) was "the house of the LORD" (1 Samuel 1:24; Psalm 24:7; 55:1). Later, the temple was known as "the house of the Lord (1 Kings 6:1; 2 Chronicles 5:13–14). This was situated in Jerusalem. Unfortunately, Israel's persistent rejection of God's authority led to conquest and exile (2 Chronicles 36:17–20) and even to the demolition of the temple itself (Matthew 24:1–2).

Today, the Church—the collection of all believers of the world—is the house of the Lord. Hebrews 10:21 mentions that Christians have a great high priest over the house of God, and 1 Peter 4:17 says, "it is time for judgment to begin at the household of God; and if it begins with us, what will be the outcome for those who do not obey the gospel of God?" Just as the psalmist vowed to seek the good of Jerusalem, so Christians should seek the good of the Church. It is for the good of the Church that believers attend regularly (Hebrews 10:25), give liberally (2 Corinthians 9:7), and pray earnestly (Matthew 9:38).