What are "Nechilos"?
Rashi citing Menachem: Nechilos, Alamos, Gitos and Yedusun are all musical instruments. The tune for each Mizmor was according to the proper instrument.
Rashi citing Shocher Tov 8: Nechilos it is an expression of Nachalah (inheritance 1 ).
Rashi: Perhaps they are troops, like [a swarm of] bees is called Nechil, and Targum Yonasan of "Nachalei Veliya'al" (Shmuel II, 22:5) is Si'as Chayavin.
Radak citing Rav Hai Gaon: This is like a swarm of bees, which is called Nechil. The tune resembled buzzing of bees.
Rashi: The word implies unlike this, and this Mizmor does not discuss inheritance!
Why did David compose this Mizmor?
Rashi: It is a Tefilah due to enemy troops that come against Yisrael; it is said for the sake of all of Yisrael.
Radak: Also this Mizmor was due to David's enemies within Yisrael, i.e. Do'eg and Achitofel (Shocher Tov).
Malbim: This Mizmor is divided into two parts. Until verse 9 explains how Tefilah should be, and how one who prays to Hashem should feel. The second part is a request that Hashem make him rest in Magelei Tzedek (23:3), and save him from his haters.
