Sometimes people think that once a person has performed sinful acts, especially acts that are grievously sinful, he must be regarded as a sinner forever. This notion runs contrary to Vaishnava philosophy.
In Bhagavad-gita (9.30–31) Lord Krishna says:
Even if one commits the most abominable action, if he is engaged in devotional service he is to be considered saintly because he is properly situated in his determination.
He quickly becomes righteous and attains lasting peace. O son of Kunti, declare it boldly that My devotee never perishes.