How did Hashem redeem David?
Malbim: Achitofel's counsel, to chase David and kill him that night, was not done.
What is "mi'Kerav Li"?
Rashi: It is from the wars that come against me. Radak - this is like "b'Yom Kerav" (78:9). The Targum of Milchamah is Karva.
Malbim: He did not allow, to come close to me, men "Asher Ein Chalifos Lamo" (refer to 55:20:5:4).
Why does it say "Ki v'Rabim Hayu Imadi"?
Rashi: He did that because many helped me, to pray for me - "v'Chol Yisrael vi'Yhudah Ohev Es David 1 " (Shmuel I, 18:16). Malbim - Hashem does not despise the Tefilah of a Rabim.
Radak #1: There were many fighting against me, and I was a small number, and Kel saved me from them.
Radak #2: The prefix Beis is extra, like the Beis in "Lachamu v'Lachami" (Mishlei 9:5). Even though they were Rabim, there were many with me, i.e. Hashem's angels - "Rabim Asher Itanu me'Asher Osam" (Melachim II, 6:16).
Perhaps Rashi means that their prayers then helped David now. That verse does not apply now - most of Yisrael supported Avshalom! (PF)