Why does it say "Lo Yachshov Hashem Lo Avon"?
Rashi: This is on condition that "v'Ein b'Rucho Remiyah" - he does not intend to return to [eat] his vomit (sin).
Radak: There is no sin at all; Hashem bears his sin if He sees the straightness of his heart; he repented with all his heart.
Radak citing his father, Malbim: A tiny minority of Tzadikim are at the highest level. He who never sinned - "Lo Yachshov Hashem Lo Avon", and his heart never even considered sinning - "v'Ein b'Rucho Remiyah."
Seforno: If the sin was for the honor of Hashem, e.g. Ya'el (had Bi'ah with Sisera in order to kill him, Hashem does not consider it a sin - Nazir 23b).
Imros Tehoros: One who is silent to one who reviles him, his Aveiros go to the reviler.
Why does it say "v'Ein b'Rucho Remiyah"?
Refer to 32:2:1:1,3.
Radak (based on Yuma 8:9): He does not intend to sin and repent.
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.