1)
What is the meaning of "Harek Chanis"?
1.
Rashi: Arm Yourself [with the spear]. This is like "Arik Charbi' (Shemos 15:9), "va'Yarek Es Chanichav" (Bereishis 14:14).
2)
What is the meaning of "u'Sgor Likras Rodefai"?
1.
Rashi: Protect between me and them, like a wall.
2.
Radak #1: Segor is a weapon.
3.
Radak #2: Close the path, so my pursuers will not catch me.
3)
Who should say to his Nefesh?
1.
Radak: You (Hashem), tell it not to fear, for You are its salvation. Strengthen it, the opposite of "v'Heveisi Morech bi'Lvavam" (Vayikra 26:36).