What does he see that he so longs for it?
Well, two things that he immediately sees are sparrows and swallows.
So this is not your typical religious understanding of the house of God, which for most means buildings of some sort. For others it might mean service of some kind, in the sense of "serving in the house of God."
But the psalmist sees sparrows and swallows. And if he sees even the birds of the sky, then he sees all of creation recovered.
The house of God ultimately is not a building, even one that is elevated on some acropolis in the sky. It is more than that; it is all of creation recovered.
But we know that the present creation is groaning until the fulfillment of the sons of God.
While this groaning is going on, it might be good to tend to the nature around us: the trees, the land; fill those bird feeders, plant and harvest. And wait with a quiet anticipation for a consummation this present world knows nothing of.
So I should not be so cast down today with my present dissatisfactions. If I am cast down, I should convert it to groaning, to longing, perhaps even to fainting, for a time when the sparrows and the swallows will, like me, find joy and rest in the house of God.
Logos2Go
Psalm 84.1-3 How lovely is your dwelling place, O LORD of hosts! My soul longs, indeed it faints for the courts of the LORD; my heart and my flesh sing for joy to the living God. Even the sparrow finds a home, and the swallow a nest for herself, where she may lay her young, at your altars, O LORD of hosts, my King and my God.
Romans 8.19-23 For the creation waits with eager longing for the revealing of the sons of God. For the creation was subjected to futility, not willingly, but because of him who subjected it, in hope that the creation itself will be set free from its bondage to decay and obtain the freedom of the glory of the children of God. For we know that the whole creation has been groaning together in the pains of childbirth until now. And not only the creation, but we ourselves, who have the firstfruits of the Spirit, groan inwardly as we wait eagerly for adoption as sons, the redemption of our bodies.
Origin: http://master-of-pentagram.blogspot.com