"In ancient times in India, once a Thief with a purpose to steal, entered the palace of a king in the dead of night and overheard the king saying to the queen, "I shall give my daughter in marriage to one of those sadhus (holy men) who are dwelling on the bank of the river," The thief thought within himself & planned: "Well, here is way to have good luck for me. I will go and sit among the sadhus (holy men) tomorrow in the disguise of a sadhu, and perhaps I may succeed in getting the king's daughter. "The next day he went & sat among the sadhus. When the king's court men came soliciting the sadhus to marry the king's daughter, none of them gave their consent to marry the king's daughter. At last they came to the thief in the guise of a sadhu, and made the same proposal to him. The thief kept quiet & did not say "No" to them. King's court men went back and told the king that there was a young sadhu who might be influenced to marry the princess and that there was no other sadhu who would consent. Then the king himself came to the sadhu by the bank of the river and earnestly entreated him to honor him by accepting his daughter in marriage.
By this time the heart of the thief had changed at the king's visit. He thought within himself: "I have only assumed the garb of a sadhu (holy man), and see!! the king himself comes to me to ask for the hand of his daughter. Who can say what better things may not be in store for me if I become a real sadhu!" These thoughts so strongly influenced him that, instead of marrying under false pretences, he began to mend his ways from that very day and exerted himself to become a true sadhu. He did not marry at all, and ultimately became one of the most pious holy man of his day. Imitating of a good thing sometimes leads to unexpected good results."
In Bhagwat Gita Lord Krishna says that one can atone for his / her sins in many ways like penance, charity etc. but there is no way more swift, fast for atonement to sins than Devotional service to God / Lord Krishna. In this regard Bhagwat Puran & Bhagwat Gita, both explain about this assurance in detail that Devotion to Lord Krishna is the supreme purifier for all the sins that a person commits in life time.
'Api chet su-duracharo
bhajate maam ananya-bhak
sadhurev sa mantavya
samyag vyvasito hi sah' (Bhagwat Gita: Chapter IX verse 30)
"Sri Krishna says to Arjuna: Even if the vilest sinner worships Me with full devotion, he should be considered a noble soul or saint; as he has taken the right step by worshipping me."
Through above verse 30, God is telling Arjuna that even if the most sinful of person worships Him with full devotion, then He considers him to be a saint only as he has rightly resolved in his life. So many times we too think that we have done many sins in life & how God shall accept us, but here God makes it very clear that once a person become devoted to Him, He does not considers that person a sinner, rather God considers that person to be a Saint as he has taken the right decision in his life to become devoted to God. Let's all be devotees of God.
'kshipram bhavti dharmatma
na me bhaktah pranashyati' (Bhagwat Gita: Chapter IX verse 31)
"Sri Krishna says to Arjuna: He speedily becomes virtuous and secures lasting peace. O son of Kunti, know it for certain that My devotee never falls."
Through above verse 31, God is telling Arjuna that such a sinful person after becoming His devotee becomes a person of good virtues and always remains in peace & such a peace is not temporary but is ever lasting. God is assuring the son of Kunti (another name of Arjuna, his disciple) that his devotee never falls again in life as He always protect him. So let's all worship the God always so that He can protect us always.
"samo ’ham sarva-bhutesu
na me dvesyo ’sti na priyah
ye bhajanti tu mam bhaktya
mayi te tesu chapy aham" (Bhagwat Gita: Chapter Nine verse 29)
"Sri Krishna says to Arjuna: I envy no one, nor am I partial to anyone. I am equal to all. But whoever renders service unto Me in devotion is a friend, is in Me, and I am also a friend to him."
Like the Sun does away with all the fog, similarly Devotion to God does away with all the sins. A man full of sin, is for certain not as much purified by penance as by the devotion to Lord Krishna. In this world there is only this path that is really appropriate & the one that is followed by the well-behaved, fearless and auspicious, saintly people; that is in surrendering oneself to Lord Krishna. So let's all be devotees of Lord Krishna.
Jai Sri Krishna.