Why does it say "Karvah"?
Radak: It is as if He is far when [Yisrael] is in Galus.
Malbim: Ge'ulah is based on kinship, like Ge'ulas Kerovim (the Mitzvah to redeem a relative sold into slavery, or to redeem land that he sold). You have Kurvah with my Nefesh, for it is a part of Eloka mi'Ma'al - no one is closer than You!
What is the meaning of "Ge'alah"?
Rashi: Redeem my Nefesh (save it).
Why did he say "Lema'an Oyvai"?
Radak: Lest they say that You do not have ability to redeem me.
Malbim: Lest they destroy him.
Why does it switch from "Ge'alah" to "Pedeni"?
Malbim: Ge'ulah is based on kinship; Pidyon is due to the matter itself. Redeem me due to my body, which is not close to You.