What is "l'Fukah"?
Rashi: It is a pitfall. This is like "u'Fik Birkayim" (Nachum 2:11). If you do so (kill Naval), you will not be able to reprimand others for murder afterwards.
Megilah 14b: David had asked to have relations with her. She said, this should not be a pitfall for you, but there will be a pitfall [with another's wife], i.e. Bas Sheva.
Malbim: If you kill Naval without reason, Sha'ul will have merit to pursue you.
What is "u'Lehoshi'a Adoni Lo"?
Rashi: It is to take vengeance yourself.
Radak citing Targum Yonasan: It is worry.
What is "Michshol Lev"? Is this not like "l'Fukah"?
Radak: Sin is a pitfall of the heart. It is repeated to strengthen the matter.
Radak citing Megilah 14b: David had asked to have relations with her. She said, you should not have Fukah of murder, and not the Michshol of Eshes Ish.
Malbim: Fik also means removal from a place where it is restrained - "Zemamo Al Tafek" (Tehilim 140:9), "Tov Yafik Ratzon me'Hashem" (Mishlei 12:2). It is accompanied with the pitfall of stumbling (sinning) in action. The same applies to "Paku Peliliyah" (Yeshayah 28:4) - "Avon Pelili" (Iyov 31:28).
