Why is it written Harbeh, and we pronounce it Herev?
Radak: These are the same. Also "Harpe Mimeni" (Shoftim 11:37) is the same as "Heref Mimeni" (Devarim 9:14).
Radak citing Shocher Tov: You did Harbeh (many) Chasadim with me; do now also, and erase my sin.
What is the meaning of "Herev Kabeseni me'Avoni"?
Radak #1: Increase Your mercy, and cleanse me from my sin.
Radak #2, Malbim: Herev is a noun; cleanse me much from my sin. Sin in the Nefesh is like a stain on a garment 1 . Malbim - Avon is a crookedness of intellect; he denies the Mitzvah or the Commander. The mistake is still in the sinner's intellect after the act.
Sha'arei Teshuvah (1:9): The Nefesh is totally purified from sin, as if it never happened, only if he purifies his heart and Ru'ach. This is like a garment that must be laundered. A little laundering removes the repugnance, but according to the great laundering it whitens.
Why did he say "Tahareni"?
Radak: The Nefesh become Tamei via sin.
Malbim: Chet is the act itself. It is attributed to the sinner after the act, only like something that touched Tum'ah; it needs Taharah due to what it touched beforehand.
