Whether one chants knowingly or unknowingly, the holy name will free one from all reactions to sinful activities:
[The Visnudutas to the Yamadutas]: As a fire burns dry grass to ashes, so the holy name of the Lord, whether chanted knowingly or unknowingly, burns to ashes, without fail, all the reactions of one’s sinful activities. If a person unaware of the effective potency of a certain medicine takes that medicine or is forced to take it, it will act even without his knowledge because its potency does not depend on the patient’s understanding.
Similarly, even though one does not know the value of chanting the holy name of the Lord, if one chants knowingly or unknowingly, the chanting will be very effective. Fire will act, regardless of whether handled by an innocent child or by someone well aware of its power. For example, if a field of straw or dry grass is set afire, either by an elderly man who knows the power of fire or by a child who does not, the grass will be burned to ashes. Similarly, one may or may not know the power of chanting the Hare Krsna mantra, but if one chants the holy name he will become free from all sinful reactions… (From Namamrta)
[The Visnudutas to the Yamadutas]: As a fire burns dry grass to ashes, so the holy name of the Lord, whether chanted knowingly or unknowingly, burns to ashes, without fail, all the reactions of one’s sinful activities. If a person unaware of the effective potency of a certain medicine takes that medicine or is forced to take it, it will act even without his knowledge because its potency does not depend on the patient’s understanding.
Similarly, even though one does not know the value of chanting the holy name of the Lord, if one chants knowingly or unknowingly, the chanting will be very effective. Fire will act, regardless of whether handled by an innocent child or by someone well aware of its power. For example, if a field of straw or dry grass is set afire, either by an elderly man who knows the power of fire or by a child who does not, the grass will be burned to ashes. Similarly, one may or may not know the power of chanting the Hare Krsna mantra, but if one chants the holy name he will become free from all sinful reactions… (From Namamrta)