Musar su Salmi 84:2

You already know that what is most desired in the service of G-d, may His Name be blessed, is desire of the heart and longing of the soul. It is concerning this that King David praised his portion saying: "As a deer yearns longingly for the water brooks, so does my soul yearn longingly to You, O G-d; My soul thirsts for G-d..." (Tehilim 42:1-2), "My soul longs, and goes out for the courtyards of G-d" (Tehilim 84:2). "My soul thirsts for You; my flesh longs for You [in an arid and thirsty land (Rashi-desert), without water]"(Tehilim 63:2).