Why does it say "Yigmeleni"?
Malbim (Tehilim 18:21): Hashavah is according to the act. Gemul is according to the love or hatred that He has for him. Gemul is always connected to excitement.
To what does "k'Tzidkasi" refer?
Rashi: This is going out to the Midbar to follow Hashem. (Rashi (8) said that the Shirah refers to miracles done for Yisrael.)
Rashi (Tehilim 18:21): I could have killed Sha'ul [in the cave,] when I cut his robe.
Radak (Tehilim 18:21): I know that I am correct, and my enemies do improperly. Therefore, save me from them!
Malbim (Tehilim 18:21): Until now, David was saved via natural Sibos - each led to another affliction. When he is saved in his merit, it is miraculous, and it is a great salvation (another affliction does not follow it).
What is the difference between "k'Tzidkasi" and "k'Vor Yadai"?
Radak (Tehilim 18:21): Tzidkasi is that I am justified [against my enemies]. Vor Yadai is cleanliness (from sin) 1 .
Malbim (Tehilim 18:21): Tzidkasi is [virtuous] actions. Vor Yadai is being passive, and not transgressing. Seemingly, Hashavah should be for Tzidkasi (actions), and Gemul for Vor Yadai (he did not do anything, but he is rewarded according to the love)! The Chidush is that Gemul is also for Tzidkasi 2 (in addition to the act), and Hashavah is even for Vor Yadai (he is rewarded for refraining from sin as if he did an act).
