The Hare Krishna mahamantra is also a prayer, for a prayer addresses the Supreme Personality of Godhead by His name and invokes good fortune by petitioning the Lord to allow one to engage in His devotional service.
Srimad Bhagavatam 4.24.69,
Of sacriﬁces I am the chanting of the holy names [japa].
Bhagavat Gita 10.25
Cleanliness is essential for making advancement in spiritual life. There are two kinds of cleanliness: external and internal. External cleanliness means taking a bath, but for internal cleanliness one has to think of Krishna always and chant Hare Krishna, Hare Krishna, Krishna Krishna, Hare Hare/ Hare Rama, Hare Rama, Rama Rama, Hare Hare. This process cleans the accumulated dust of past karma from the mind.
Bhagavad Gita 13.8-12,
The holy name of Krishna is so attractive that anyone who chants it — including all living entities, moving and nonmoving, and even Lord Krishna Himself — becomes imbued with love of Krishna. This is the effect of chanting the Hare Krishna maha-mantra.
Chaitanya Caritamrta, Antya Lila 3.268,
One need only chant the Hare Krishna mahamantra. Everyone engaged in the practice of chanting the Hare Krishna mahamantra will be completely cleansed, from the core of his heart, and be saved from the cycle of birth and death.
Srimad Bhagavatam 7.6.1,
You just accept the holy name, then Nityananda Prabhu will be responsible for taking you across this material world.