Why does it say that they be satiated from the fatness of Your house?
Radak: This is in the world to come, and the world of Neshamos and angels. It is Beis Hashem, just like it is called Heichal Hashem, Har Kodsho, Har Hashem and No'am Hashem, like I explained (11:4, 15:1, 27:4).
Malbim: All offshoots of nature are outside of Beis Hashem, in the outer courtyards (nature). Human Nefashos are Hashem's household, and eat on His table. Their food and water are not physical, rather, they are the fatness of His house - bread of Abirim (angels), and their drink is of the river of supreme pleasure. This is a parable for Divine influence if His Torah, Mitzvos, designation of His Shechinah and Nevu'ah. through this, one merits all spiritual attributes. What fool will question reasons of Mitzvos Bein Adam l'Makom?! Since man is tied to Hashem this way, surely he must guard His Mitzvos, which are means to this end! They are the food and water that satiate the Nefesh Bas Elokim.
What is "Adanecha"?
Radak: It is knowing Hashem - the good that is not followed by evil, and the satiation that is not followed by hunger and thirst. It is called Nachal Adanecha, for it is abundant like a river.
Why does it say "Sashkem"?
Radak: You will help them to know [You].
