Rashi on Psalms
A song of David The Rabbis said: Wherever it says: “A song of David,” he would play [his musical instrument] and afterwards the Shechinah would rest on him. It is a song to bring the holy spirit upon David. And, wherever it says: “Of David, a song,” the Shechinah rested on him [first] and then he recited a song.
Rashi on Psalms
The Lord is my shepherd In this desert where I am going, [therefore] I am confident that I will lack nothing.