What does Psalm 122:4 mean?

Jacob was renamed "Israel" by God (Genesis 32:27–28). Jacob was a descendant of Abraham (Matthew 1:2) and his twelve sons were the origin of the twelve tribes of Israel (Genesis 35:23–26). All men of the nation of Israel were expected to attend three annual feasts at the center of worship (Deuteronomy 16:16). These times of prayer and gratitude were Passover, Pentecost, and Tabernacles (Exodus 23:14–17).

At the time this psalm was written, the "house of the Lord" (Psalm 122:1) was the temple in Jerusalem (1 Kings 6:1). Jerusalem was situated on and around Zion, which had once been a mountain stronghold captured by David (2 Samuel 5:6–10). Traveling to Jerusalem literally meant moving "up" to a higher elevation.

The Feast of Passover commemorated the Lord's passing over every house in Egypt that displayed the blood of a spotless lamb on the door. Houses that did not display the blood experienced the death of its firstborn (Exodus 12). The Feast of Pentecost involved the gathering of the harvest which pictured the gathering of believers into the body of Christ (Leviticus 23:15–16; Acts 2; Ephesians 1:11–14). The Feast of Tabernacles (Leviticus 23:41–42) commemorated Israel's living in tents during their wilderness journey from Egypt to Canaan. It pictures Christians living in temporary, fragile mortal bodies until Jesus raptures and resurrects them (1 Corinthians 15:50–52; 2 Corinthians 5:1–4).