What is the Chidush that he went in Hashem's ways?
Radak #1: Because I guarded all the Mitzvos, Hashem guarded me from my enemies.
Radak #2: When Sha'ul pursued me, I did not kill him when I had the opportunity. Even though a Nirdaf may kill his pursuer, a king is different (one may not kill him).
Malbim: The Tzedek that I did was not because intellect and etiquette obligate it; if so, I would be rewarded only for the deed itself. Rather, I guarded it because they are Darchei Hashem, to go in His ways and resemble him. Therefore, I am worthy of Gemul according to my love and Deveikus, that I went in His path and clung to Him.
What is the meaning of "v'Lo Rashati me'Elokai"?
Radak #1: I did not do b'Resha (b'Mezid); if I left His path, it was Shogeg.
Radak #2: Refer to 18:22:1:2.
Radak (Shmuel II, 22:22): I did not leave the ways of my G-d. "Darchei" refers to both Hashem and Elokai.
Radak (Shmuel II, 22:22, based on Targum Yonasan there): I did not go in evil in front of my G-d.
Malbim: I refrained from evil not due to intellect, or due to my nature, rather, due to Elokai - His commands, even though my Yetzer ha'Ra tempted me to do evil. I deserve reward, like one who had opportunity to sin and overcame his desire. He is rewarded like one who did a Mitzvah.
