According to Osho, sin is the ego's isolation—trying to purify oneself without the Whole—while virtue is egolessness born of prayerful surrender. Prayer is the medicine: it dissolves sin and prevents "virtue" from becoming pride. A prayerless do-gooder turns good deeds into sin; a humble, praying "sinner" opens to grace, and true virtue flowers as gratitude.
Sin is proud separateness; virtue is humble togetherness with the Whole, asked for through prayer.