How did he stray?
Radak: He erred about this knowledge, that I still do not know. I am like a lost sheep that does not know to return to where it lies. So my Nefesh does not know to return to its foundation.
Malbim: I flee Sha'ul, and stray in Chutz la'Aretz.
Why does it say "Bakesh Avdecha"?
Radak: Just like a faithful shepherd seeks a lost sheep until he finds it and returns it to where it lies, so seek me until You return me to my foundation, i.e. of the Nefesh.
Malbim: Return me to Eretz Yisrael.
Why does it say "Ki Mitzvosecha Lo Shachachti"?
Radak: Just like I did not forget, You should not forget me, and rather, You should seek me.
Malbim: Even though I forgot where I lie and graze, I did not forget Your Mitzvos.
