I need to know the opposite of sin, other than virtue which I don't think is right.
How about righteousness?
right·eous·ness [rahy-chuhs-nis] Show IPA noun 1. the quality or state of being righteous. 2. righteous conduct. 3. the quality or state of being just or rightful: They came to realize the righteousness of her position on the matter.
— adj 1. a. characterized by, proceeding from, or in accordance with accepted standards of morality, justice, or uprightness; virtuous: a righteous man b. ( as collective noun ; preceded by the ): the righteous 2. morally justifiable or right, esp from one's own point of view: righteous indignation
good deed maybe?
deed: something that is done, performed, or accomplished; act: a good deed
If we are talking Christian theology, and sin as mass noun rather than the countable noun or verb, I would suggest grace as a possible antonym.