The elephant may take a very nice bath in the river, but as soon as it comes onto the bank, it throws dirt all over its body. What, then is the value of its bathing? Similarly, many spiritual practitioners chant the Hare Krishna Mahamantra and at the same time commit many forbidden things, thinking that their chanting will counteract their offenses.
The chanting of the Hare Krishna mantra is recommended even for persons who commit offenses, because if they continue chanting they will gradually chant offenselessly.
Purport on Srimad Bhagavatam 6.3.24
By inducing the offenders to chant the Hare Krishna mantra, Lord Chaitanya Mahaprabhu exemplified the success of the Krishna consciousness movement.
Purport on Chaitanya Caritamrta Adi Lila 7.150
Whole things start with the mind. If mind is not purified then the words, through the words and through the body we will be committing sins and offences.
Of the nine processes of devotional service, the most important is to always chant the holy name of the Lord. If one does so, avoiding the ten kinds of offenses, one very easily obtained the most valuable love of Godhead.
Chaitanya Caritamrta Antya Lila 4.71
To not feel joyful upon seeing a Vaisnava is an offense arising from a heart immersed in envious feelings.