Why did he say "Kol Mitzvosecha Emunah"?
Radak: They are Emes.
Malbim: The foundation of the Mitzvos is to believe in the Commander and His Mitzvos, and not to investigate and analyze [why we should keep them]. Rather, one does amidst Emunah.
Why did he say "Sheker Redafuni"?
Rashi: My enemies pursued to forbid me based on Sheker! "Mo'avi" [may not enter Kahal Yisrael], and not a Mo'avis.
Malbim: They say that it is Sheker (that Mitzvos are Emunah); rather, they investigate and theorize about matters of Mitzvos, and via this they transgress them.
Why should Hashem help him?
Radak: You commanded not to oppress the weak, and You judge their case - "Oseh Mishpat Ger Yasom v'Almanah" (Devarim 10:18). If so, You should help me, for they pursue me with Sheker and without reason!
Malbim: They pursue me for guarding the Mitzvos with Emunah!