1)
Will David be the shepherd?
1.
Rashi: It will be a king from his seed.
2.
Radak: It will be the Mashi'ach who will stand from his seed at the time of the salvation.
2)
Above (15) it said that Hashem Himself will shepherd Yisrael. Why does it say here that the shepherd will be from David?
1.
Malbim: The king from David will be in place of Hashem. There are three levels. First Hashem will appoint someone from Beis David to conduct Yisrael, to force them to do Mishpat and Tzedakah. After, he will be the shepherd ? they will willingly accept his conduct and learn from him. And finally, (refer to 34:24:1:1).