MIDRASH TEHILLIM
1.....(4.6)
The phrases for the leader; with instrumental music
Introduce this Psalm with three varieties of praise:
-with the leading of the music
-with the playing upon the instruments
-with the singing of the Psalm.
The phrase - string music, refers to prophecy, for it is said: "And now bring me a musician." And it was that when the musician played, the hand of the Lord came upon him." (Melachim II - II Kings 3:15)
"The leader" - most capable of glorifying Him, whose glory endures forever and ever.
"For the leader" - (lamnatzeyach), which means literally - To Him who wins, may be also read as - (limnutzach), To Him who lets himself be won over by His creatures.
A mortal king, when vanquished by one of his subjects is angry, but the Holy one, when vanquished by one of his creatures, rejoices, as it is said: "He intended to destroy them [and would have] were it not that Moses, His chosen one, stood before Him in the breach to return His wrath from destroying." (Tehillim 106:23)