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,
Any person who is chanting the holy names of Krishna (Hare Krishna, Hare Krishna, Krishna Krishna, Hare Hare/ Hare Rama, Hare Rama, Rama Rama, Hare Hare) in course of chanting without offenses feels some transcendental pleasure and very quickly becomes puriﬁed of all material contamination.
Bhagavat Gita 9.2,
Happiness derived from a combination of the senses and the sense objects is always a cause of distress and should be avoided by all means.
Bhagavad Gita 18.38,
The Bhagavad-gita can be consulted in all critical times, not only for solace from all kinds of mental agonies, but also for the way out of great entanglements which may embarrass one in some critical hour.
Srimad Bhagavatam 1.15.27,
Bhagavad-gita is the instruction given by Krishna, and Srimad-Bhagavatam is the book containing topics exclusively about Krishna and His devotees. These two books are the special nectar of the words of Krishna.
Srimad Bhagavatam 4.4.44,
To show them special mercy, I, dwelling in their hearts, destroy with the shining lamp of knowledge the darkness born of ignorance.
Bhagavad Gita 10.11,