Ramban and others ask why hester panim should be Hashem's response once the chotei has acknowledged that punishment is not a chance occurance, but comes "al ki ain Elokai b'kirbi", because the chotei has drifted far from Hashem (see previous post). The Seforno's pshat answers this question and sheds light on the whole process of tshuvah. "Ain Elokai b'kirbi" is not an admission, but a part of the corrupt outlook of the sinner - Hashem has abandoned the world and abandoned man to suffer in his own morass. This is the negation of the concept of "imo anochi b'tzarah", the belief that even in sin, Hashem is always with us. The resultant hester panim is a perfect midah k'neged midah of the sinner's own corrupt belief system.
Rav Kook writes that the greatest obstacle to tshuvah is our lack of appreciation of its effectiveness. R' Nachman also bemoans the tremendous damage of ye'ush, despair, which can far exceed the harm of sin itself. The hashkafa of "ain Elokai b'kirbi", of abandonment and hopelessness, is what prevents one from seizing the opportunity to grow.
The Midrash teaches that unlike someone preparing for a solemn death row case in court, a Jew prepares for Rosh haShana with simcha and anticipation. The Koznitzer Maggid quotes R' Dov Ber as explaining "kosveinu l'chaim" means writing in our hearts - we beg Hashem to let us believe in the power of tshuvah so we approach the yom hadin with confidence of mechila v'kapparah. It is not sin alone which condemns the rasha, because "ain tzadik ba'aretz", no one alive has not sinned, but what condemns the rasha is the loss of hope and connection to the power of renewal.