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 the book Surrender unto Me, Bhurijana Dasa comments on Bhagavad-gita 4.36–37, with references to the commentary of Srila Visvanatha Cakravarti Thakura.
36. Even if you are considered to be the most sinful of all sinners, when you are situated in the boat of transcendental knowledge you will be able to cross over the ocean of miseries.
In Chapter One, Arjuna feared sin and its resultant suffering. Krsna herein tells Arjuna the cure is transcendental knowledge, not fleeing the battlefield.
The words api cet (“even if”) are used when one accepts the occurrence of an unlikely or apparently self-contradictory event. Three questions could be asked, as posed by Srila Visvanatha Cakravarti Thakura: If someone is acting so sinfully, how can his heart become purified? And without such purification, how can he develop knowledge? And if he has developed knowledge, how can he act with such impropriety?
Krsna is thus describing this “api cet” situation to glorify the purifying effects of transcendental knowledge.
37.As a blazing fire turns firewood to ashes, O Arjuna, so does the fire of knowledge burn to ashes all reactions to material activities.
Srila Visvanatha Cakravarti Thakura comments: “Krsna says, ‘For one whose heart has become purified, I destroy completely whatever karma has already been generated with the exception of his parabdha-karma.‘ ”
Transcendental knowledge thus destroys all reactions, both pious and sinful; all, that is, except prarabdha-karma, or matured reactions, such as one’s present material body.