English Basic Explanation - Chapter 84
This Psalm was composed as a prayer to be recited during exile, and expresses the Jew's longing for the restoration of the Bet Ha'mikdash. The Psalmists (the children or descendants of Korah) describe their overwhelming desire to once again frequent the sacred site of the Temple, and their frustration over the fact that birds can make their nests on this holy site, while Am Yisrael is still unable to step foot on the Temple Mount.
Chapter 84 contains the famous verse "Ashre Yosheve Betecha" (verse 5), which speaks of the good fortune of those who have the ability to "reside" in the Bet Ha'mikdash. The Jew in exile can only envy his predecessors who were privileged to visit the Temple and experience this direct encounter with the Shechina (Divine Presence). As the authors describe in verse 11, a single day spent in the Mikdash is more valuable than one thousand days spent elsewhere, and standing by the entrance to the Temple is preferable to full-fledged residence in the home of a wicked person. The inspiration that can be drawn from a visit to the Bet Ha'mikdash is worth far more than any worldly delights that could be enjoyed in other places.
This prayer concludes with the exclamation, "Lord of Hosts – fortunate is the man who trusts in You!" (verse 13). The Radak explains that this verse addresses the Jew who might be led to despair by the long duration of exile. He is bidden to retain his faith in God's promise to restore the Mikdash, rather than lose hope. Those who hold out faith in the ultimate rebuilding of the Temple are indeed "fortunate" as they will be privileged to one day fulfill their aspirations of frequenting the sacred site and delight in the presence of the Shechina.