Source: The Gospel of Sri Ramakrishna
M: "You once said that one who constantly talks of his sin really becomes a sinner; he cannot extricate himself from sin. But if a man has firm faith that he is the son of God, then he makes rapid strides in spiritual life."
MASTER: "Yes, faith. What tremendous faith Krishnakishore had! He used to say: 'I have spoken the name of God once. That is enough. How can I remain a sinner? I have become pure and stainless.' One day Haladhari said: 'Even Ajamila had to perform austerities to gratify God. Can one receive the grace of God without austerities? What will one gain by speaking the name of Narayana only once?' At these remarks Krishnakishore's anger knew no bounds. The next time he came to this garden to pick flowers he wouldn't even look at Haladhari.
"Haladhari's father was a great devotee. At bathing-time he would stand waist-deep in the water and meditate on God, uttering the sacred mantra; then the tears would flow from his eyes.
Krishnakishore's faith in God
"One day a holy man came to the bathing-place on the Ganges at Ariadaha. We talked about seeing him. Haladhari said, 'What shall we gain by seeing the body of a man, a mere cage made of the five elements?' Krishnakishore heard about it and said: 'What? Did Haladhari ask what would be gained by visiting a holy man? By repeating the name of Krishna or Rama a man transforms his physical body into a spiritual body. To such a man everything is the embodiment of Spirit. To him Krishna is the embodiment of Spirit, and His sacred Abode is the embodiment of Spirit.' He also said, 'A man who utters the name of Krishna or Rama even once reaps the result of a hundred sandhyas.'
"One of his sons chanted the name of Rama on his death-bed. Krishnakishore said, 'He has nothing to worry about; he has chanted the name of Rama.' But now and then he wept. After all, it was the death of his own son. "Nothing whatsoever is achieved by the performance of worship, japa, and devotions, without faith. Isn't that so?"
M: "Yes, sir. That is true."
Please check these: Excerpts from a discourse by our Sri Sri Muralidhara Swamiji
Those who chant the Mahamantra even once in this Kali Yuga are assured of 'Moksha' (liberation)
The glory of the Divine Names cannot be understood by logic, reasoning or argument
Japa even once uttered has its own good effect, whether the individual is aware or not.
Chant the Mahamantra Nama kirtan :
Hare Rama Hare Rama Rama Rama Hare Hare
Hare Krishna Hare Krishna Krishna Krishna Hare Hare