Dovid Hamelech Davened for Future Generations: Sefer M’Ohr Vashemesh (Parshas Mishpatim) says in the name of the Radak that Dovid Hamelech davened for everything that Klal Yisroel would need until the coming of Moshiach. He davened for every sick person to be healed, for every healthy person not to become sick, for everyone to have parnassah, and for all harsh decrees to be rescinded. And all of these prayers are hinted to in Tehillim.