Why did he do Avel?
Radak, based on Kidushin 40b: This refers to one who one who regrets his earlier Mitzvos. Amidst love for worldly desires, he regrets that he did not do like his heart's desire in the past. Even so, he trusts that his prior virtue will help him!
Malbim: I told him "Chayo Yichyeh", for he is totally virtuous. He relied on this, and sinned. He thought that because he has previous virtue and many good deeds, he can sin and it will not harm him. This is like Shlomo said, I will increase [wives] and I will not veer [my heart from Hashem]. The virtue is a reason why he does Avel! He thinks that because he fasts and prays, he can steal and oppress, and there is no sin. Therefore his virtue will not be recalled.
What is the meaning of "Lo Sizacharnah"?
Rashi: It will not save him from punishment for this sin.
Malbim: Refer to 33:13:1:2.
